# Post-Earthquake Fire Punching Shear Behavior of GFRP-Reinforced Slab-Column Connections

Authors: Tesfaye Alemu Mohammed; Shewarega Shirtaga
Journal: Advances in Civil Engineering
 (2023)

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## Abstract

It is not uncommon for reinforced concrete slab-column assembly to experience a punching brittle shear failure type under seismic loading. This research work numerically investigates the punching shear behavior of interior GFRP-reinforcedslab-column connections under post-earthquake fire. Two experimental results reported in the article were used for validation analysis using ANSYS nonlinear finite element software program. Further, parametric studies on influential variables such as fire exposure duration, concrete grade, slab thickness, fire exposed surface, and column aspect ratio were performed to get insight into the post-earthquake fire behavior of GFRP-reinforcedslab-column connections. Finite element analysis results showed decreasing fire exposure duration, enhancing grades of concrete, increasing slab thickness, minimizing fire exposure surfaces, and increasing column aspect ratio, which improved the punching shear capacity of GFRP-reinforced slab columns. Moreover, increasing slab thickness provided good performance against post-earthquake fire loading as compared to enhancing concrete grades in GFRP-reinforcedslab-column assemblies. The research concludes that it is crucial to take post-earthquake fire into account when designing structures to ensure no collapse safety design requirements.


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## Body

## 1. Introduction

Slab-column connections, also known as flat slab constructions, are assemblies of a building in which reinforced concrete floor slabs are directly attached to columns without the use of beams. Flat slab constructions are popular in residential buildings and car parking garages partly due to their advantages, such as reduced story heights, flat finishes, fast construction times, and flexibility to put columns in a variety of positions [1]. However, despite the aforementioned advantages of flat slab construction, there is also a risk that a hazardous brittle failure mode, namely, punching shear failure, is likely to occur if shear stresses in the floor reach critical levels and a RC column punches through a slab (Figure 1). The main cause of this failure is a load being transferred directly to a column in shear through a relatively small area of concrete [1].Figure 1
Flat plate.As opposed to conventional steel rebars, glass fiber-reinforced polymer (GFRP) has immunity against corrosion, light self-weight, and high tensile strength. This characteristics appeal for its use as an alternative construction material [2]. In contrary, GFRP rebars have lower elastic stiffness, resulting in a lower punching shear capacity of GFRP-RC slab-column connections as compared to corresponding steel rebar counter parts with the same steel reinforcement ratio [2], and despite this, GFRP rebars have been shown to resist seismic loads in slab-column connections [3].Recent studies [4–6] investigated the punching shear behavior of interior FRP-RC slab-column connections with various forms of FRP shear reinforcement under monotonic load. Similarly, few researchers [3, 7–9] studied the effectiveness and contribution of GFRP stirrups as shear reinforcement in two-way slabs under lateral cyclic load. Their findings revealed that the use of GFRP stirrups resulted in a more flexible punching shear failure mechanism.Numerous studies [1–9] investigated the punching shear behavior of GFRP-reinforcedslab-column connections at ambient temperatures, and there is perceived void in the article on post-earthquake fire punching shear behavior of GFRP-reinforcedslab-column connections. Secondary fire loading followed by an earthquake action poses a major threat to structural integrity of a member and needs in detail study as a structural member’s singular response for only fire, and only earthquake is different as compared to combined post-earthquake fire scenario [10].Prior studies on structural responses to fire have primarily focused on steel members, RC flat slabs, RC columns, and RC beams. However, it ignored the GFRP-reinforcedslab-column connection that was exposed to post-earthquake fire. Long-termpost-earthquake fire exposure can result in significant thermal gradients through the GFRP-reinforcedslab-column connections, which could eventually cause punching failure of the connections under post-earthquake fire loading conditions. By presenting numerical modeling of a GFRP-reinforcedslab-column connection subjected to the post-earthquake fire, this research fills in a significant knowledge gap on the subject. This information may ultimately contribute to the improvement of analysis tools for the rational load-based design of GFRP-reinforced concrete structures under post-earthquake fire loading.The present research work fills in perceived void in the article by studying post-earthquake fire punching shear behavior of GFRP-reinforcedslab-column connections. Two experimental data reported in recent articles [3, 11] were used for validation and verification of developed 3D FE models using the ANSYS nonlinear finite element software program. Further, parametric studies were performed on influential variables such as post-earthquake fire exposure duration, concrete grade, slab thickness, fire exposed surface, and column aspect ratio to get insight into the punching shear behavior of GFRP-reinforcedslab-column connections subjected to post-earthquake fire loading.


## 2. Materials and Methodology

Post-earthquake fire was modeled using ANSYS [12] coupled-field analysis methodology. Solutions and procedures associated with a particular engineering discipline are referred to as coupled-field physics analyses when the input of one physics analysis depends on the results of another analysis. The complete analyses are defined as coupled-field analysis. Thus, a sequentially coupled thermal-stress analysis is conducted in ANSYS in view of the fact that the stress/displacement solution is dependent on a temperature field, but there is no inverse dependency.Coupled-field analysis involves a sequential analysis where first fire loading is applied and finite element analysis is performed to evaluate nodal temperatures of a FE model. This is followed by the application of structural loading and the execution of finite element analysis to evaluate the residual strength, stress, and deformation of a structure. This coupled-field sequential analysis shows the response of a structure subjected to post-earthquake fire [12].Since there are no reported experimental works on punching shear behavior of slab subjected to post-earthquake fire, the authors of this study used two experimental works reported in the article for the validation and verification of developed FE models. One experimental work is on GFRP-reinforcedslab-column connection subjected to lateral loading [3], and the second experimental work is on reinforced concrete flat slab subjected to fire loading [11]. When combined, the aforementioned two cases characterize the behavior of RC slab under a post-earthquake fire scenario. In coming sections, details of the two experimental works employed for validation and verification FEA are presented.


### 2.1. Description of Part-I Specimen for FE Model Validation and Verification: GFRP-ReinforcedSlab-Column Connection under Lateral Cyclic Loading

Interior GFRP-reinforcedslab-column connection with GFRP shear reinforcement provided at 2 d from the face of a column, experimentally tested by [3] under reversed cyclic loading, was selected for validation and verification FEA of earthquake loading. This adequately designed GFRP-reinforcedslab-column connection specimen was also used as a control specimen.Experimental tests were conducted by [3] for shear-governedslab-column connections reinforced with glass fiber-reinforced polymer bars constructed without and with GFRP shear reinforcement. From these tested specimens, slab-column connections with GFR shear reinforcement were used to capture the effects of shear reinforcement as well as other investigated parameters for NLFEA. Also, from this shear reinforcement, provided slab-column connections used to provide shear reinforcement up to 2 d from the face of columns, this specimen is collapsed at 4.5% drifts, so we use this to capture the computational times of NLFEA compared to others shear reinforcement slab-column connection sample.


#### 2.1.1. Details of Part-I Specimen

The geometry and reinforcement detailing characteristics of the developed FE model were identical to experimental work conducted by [3] on full-scaleGFRP-reinforcedslab-column connections with GFRP shear reinforcement provided at 2 d from the face of the column. The slab-column connection has a geometric dimension of 2500 mm × 2500 mm with a thickness of 200 mm and a 300 mm square column, extending 700 mm above and below slab surfaces (Figure 2). Sand-coated GFRP reinforcing bars (10 no. 15 and 14 no. 20) were used for flexural reinforcement at top and bottom of a slab, whereas closed GFRP shear reinforcement (16 no. 10) was also used in the slab. Moreover, six longitudinal deformed steel bars (25 M) and 16 closed ties (10 M) were used in columns. The reinforcement configurations of the specimen are shown in Figure 2 with bottom and top reinforcement placed symmetrically in each orthogonal direction.Figure 2
Geometry and reinforcement configuration of part-I slab-column connection specimen [3]. (a) Geometry (mm). (b) Reinforcement detailing.
(a)(b)


#### 2.1.2. Material Properties of Part-I Specimen

Material properties employed for FE models were similar to experimental works conducted by [3] on full-scaleGFRP-reinforcedslab-column connections. Elastic module values of both bottom and top GFRP flexural reinforcements of a slab were 64.9 and 62.6 GPa, respectively, whereas elastic modulus of the GFRP shear reinforcement for the slab is 45 GPa. The yield strength of the main steel column rebar and steel column shear reinforcement was 4706 MPa and 2806 MPa, respectively. A compressive strength of concrete used for both slab and column was 45 MPa. Detailed material properties of concrete, GFRP, and steel rebar reinforcement are shown in Table 1.Table 1
Material properties of concrete, GFRP, and steel rebar reinforcement [3].
MaterialsConcretefc (MPa)fct (MPa)453.75Reinforcement typeBar sizeBar Փ (mm)Area (mm2)Elastic modulus (GPa)Ultimate tensile strength (MPa)Characteristics tensile strength (MPa)Ultimate tensile elongation (%)GFRP main slab barNo. 1515.919962.6123911841.89No. 2019.128564.9133410792.07Column steel bar25 M25.2490200Fu = 620Fy = 470εy = 0.24Steel stirrup10 M11.3100.2200—280—GFRP stirrupNo. 109.4971459485040.53


### 2.2. Finite Element Modeling of Part-I Specimen Using ANSYS Software Program

#### 2.2.1. Element Types

CPT215 element type from ANSYS element library was used to model the concrete and steel loading plates. CPT215 element is a brick element with eight nodes and has three degrees of freedom per nodes. The element has the capability of stress stiffening, large deflection, elasticity, and large strain [12].Reinf264 element from ANSYS element library was employed to model steel and GFRP reinforcement. Reinf264 element is a uniaxial tension and compression element with two nodes. Reinf264 element has three translational degrees of freedom compatible with the parent concrete CPT 215 element [12]. This element is also capable of simulating nonlinearity and plastic deformations.


#### 2.2.2. Material Types

A coupled damage-plasticity microplane model from ANSYS material library was used to model concrete material. A coupled damage-plasticity microplane model was formulated from research works of [13–15], where concrete material is characterized through uniaxial stress-strain laws of various individual planes [12].For the concrete, a coupled regularized damage-plasticity microplane model was used [13]. In this model, uniaxial stress vs. strain equations are applied to several small planes, referred to as microplanes, to approximate the material behavior. This method was used to capture the concrete’s inelastic behavior and get around the analysis’s numerical instability caused by the material’s strain softening [14]. A smooth, three-surface Drucker–Prager microplane with tension and compression cap surfaces serves as the definition for the coupled damage-plasticity microplane model. Limiting the yield surface’s expansion in both tension and compression is the fundamental benefit of using two cap surfaces.The use of a coupled damage-plasticity microplane model requires thirteen concrete material inputs out of which seven parameters are related to plasticity, four to damage, and two to nonlocal parameter. Parameters related to plasticity behavior of concrete includes Drucker–Prager yield function, compression cap, and hardening parameters [14, 15]. Drucker–Prager yield function parameters include listing of uniaxial compressive strength, biaxial compressive strength, and uniaxial tensile strength. The compression cap parameter listing refers to the abscissa intersection point between the compression cap and Drucker–Prager yield function and the ratio between the major and minor axes of the cap. Concrete plasticity hardening parameter listings are hardening material constant and tension cap hardening constant. The four damage parameter constants include tension and compression damage thresholds and tension and compression damage evolution constants. Last, two nonlocal parameters definition consisting of the nonlocal interaction range parameter and overnonlocal averaging parameter completes concrete material modeling using the coupled damage-plasticity microplane model. Table 2 presents details of concrete coupled damage-plasticity microplane model inputs for the Part-I FE model.Table 2
Concrete coupled damage-plasticity microplane model inputs.
ConstantValueE (MPa)36000Nu0.18C1 (MPa)45C2 (MPa)51.7C3 (MPa)3.8159C41C54000C6−31.5C72C80C90.00002C103000C112000C1600m2.5A bilinear isotropic and linear-elastic material model from ANSYS material library was used to characterize conventional steel rebars and GFRP reinforcement. Poisson’s ratios of 0.3 and 0.25 were employed for the steel and GFRP bars, respectively. Modulus of elasticity and Poisson’s ratio values of 200 GPa and 0.3 were used for steel loading plates material modeling. Table1 presents detailed material inputs of steel rebars, GFRP flexural bars, and shear stirrups. A perfect bond was assumed between the concrete and embedded rebar reinforcements.


#### 2.2.3. Model Geometry, Boundary Conditions, and Loading

Taking advantage of the symmetry, half of GFRP-reinforcedslab-column connection subassemblage was modeled using ANSYS mechanical APDL. Half of the entire model was considered in the longitudinal section of full interior slab-column connection. This approach leads to a reduction in computational time and storage disk space requirement.A boundary condition was applied at the plane of symmetry and support locations to constrain nodes. At the plane of symmetry alongx-axis, translation degree of freedom (DOF) in X -direction (Ux) was set to zero, and at a support location similar to experimental set up [3], all translation DOF Ux, Uy, and Uz were set to zero. Moreover, identical to experimental set up [3], axial loading of 70 KN was applied at the top of a column to simulate gravity loading. Displacement-controlled FE analysis was performed by applying 60.75 mm of lateral displacement at a height of 675 mm from the center of a slab in the opposite direction on both top and bottom of columns. Figure 3 presents the loadings and boundary conditions of the developed FE model.Figure 3
Geometry, meshing, loading, and boundary conditions of part-I specimen.


### 2.3. Description of Part-II Specimen for FE Model Validation and Verification: Punching Shear Strength of Reinforced Concrete Flat Slab Subjected to Fire Loading

In this section, experimental data reported by [11] on punching shear strength of reinforced concrete flat slab subjected to fire on their tension was chosen for validation and verification FEA of fire loading. This Part-II FE validation analysis complements the Part-I FE model validation on the application of fire loading. Details of the specimen are presented in the next few subsections.


#### 2.3.1. Detailing of the Specimen

A full-scale RC flat slab specimen chosen for FE validation analysis on fire loading has width and length geometric dimensions of 1100 × 1100 mm. The flat slab has 100 mm thickness and a 150 mm square column extending 400 mm height above the flat slab surface. The flat slab was reinforced with 11 Φ 10 mm rebars in the tension side and 7 Φ 10 mm in the compression side. Similarly, the column was detailed with 4 Φ 10 longitudinal rebars and 4 Φ 8 mm stirrups. Figure4 shows rebar detailing of Part-II specimen.Figure 4
Reinforcement detailing of part-II specimen [11]. (a) Compression reinforcement. (b) Tension reinforcement. (c) Center line section.
(a)(b)(c)


#### 2.3.2. Material Properties of Part-II Specimen

RC flat slab Part-II specimen was reinforced with 10 mm diameter deformed rebars, whereas column stirrups were made of 8 mm diameter plain rebars. The deformed and plain bars had yield stresses of 410 and 270 MPa, respectively. The flat slab had concrete compressive strength of 25 MPa. Table3 shows details of flat slab concrete and rebar material properties.Table 3
Material properties of concrete and reinforcement [11].
MaterialsConcreteCompressive strength, fc (MPa)25ReinforcementBar sizeBar diam. (mm)Elastic tensile modulus (GPa)Yield strength in (MPa)Steel main barΦ1010200410Steel stirrupΦ88200270


### 2.4. Finite Element Modeling of Part-II Specimen Using ANSYS Software Program

A sequential coupled-field analysis was performed to simulate fire loading using ANSYS software program. First, heat transfer thermal analysis is performed followed by coupled structural analysis. Briefly, temperatures at each node of a FE model are evaluated from thermal analysis and used as input data in following structural analysis. Finally, structural evaluations are performed to determine the structural collapse that occurs when a structure is exposed to both fire and applied forces [16].


#### 2.4.1. Fire Loading

In the present study, applied fire loading was characterized using fire loading curve from the international standardization organization (ISO834) [17]. The fire loading curve (Figure 5) is characterized using the following equation:(1)T=345log8t+1+20,where T indicates temperature, in degrees celsius, and t indicates time, in minutes.Figure 5
ISO-834 fire curve [17].


#### 2.4.2. Sequential Coupled-Field Finite Element Analysis

Heat transfer is a measure of thermal load which simulates fire loading. The amount of heat transferred through a body is referred to as heat transfer. When temperatures of two systems differ, heat is transferred from a higher temperature to a lower temperature, eventually forming the two systems back into equilibrium through conduction, convection, or radiation mechanism [18].Transient thermal analysis where material properties change over time as a function of temperature was executed to simulate fire loading. Transient thermal analysis requires inputs such as density, thermal conductivity, and specific heat of a material. Aforementioned material inputs were entered as a function of temperature using reduction factors from [19].In multiphysics simulations, ANSYS software program performs finite element numerical analysis of reinforced concrete slabs subjected to fire in two steps: first, transient thermal analysis is performed, followed by coupled structural analysis [12, 20].Element types, SOLID70 and SURF152, from ANSYS element library were used to model concrete and target fire loading surface area in transient thermal FE analyses, respectively. Eurocode [19] was used to define the thermal material properties of concrete. Applying sequential coupled-field analysis technique requires first transient thermal analysis to be completed, and this is followed up performing structural analysis using nodal temperature results from former analysis as an input to latter FE structural analysis [12, 21]. However, FE model and geometry must remain the same in both analysis types.Perfect bond was assumed between concrete and GFRP rebars. This assumption implies that GFRP rebar nodes in a FE model have identical nodal temperature value with parent concrete element.In sequential coupled-field analysis, four procedures need to be executed while moving from thermal analysis to coupled structural analysis. First, thermal element types are switched with equivalent structural elements. In this study, thermal element SOLID70 was swapped with SOLID185 and CPT 215 structural elements [12]. Second, concrete and steel rebar mechanical are input as a function of temperature. In the present article, reduction factors from Eurocode [19] were employed to define concrete and steel rebar material properties as a function of temperature. Third, SURF152 elements are deleted from the FE model. SURF152 element was used to define target fire exposed external flat slab concrete surfaces in thermal analysis, and they are no longer required in a follow up coupled structural analysis.Finally, in fourth step, boundary conditions and structural load are applied before performing coupled structural FEA. In this study, boundary conditions were applied at plane of symmetry (UX = 0) and support locations (Ux, Uy, and Uz = 0) to constrain respective nodal translation degrees of freedom. Next, structural lateral and axial loads were applied, and coupled structural analysis was performed to learn the punching shear behavior of GFRP-reinforcedslab-column connection subjected to post-earthquake fire loading.


#### 2.4.3. Geometry, Boundary Conditions, and Loading

Taking advantage of symmetry, a half-full model according to experimental details [11] was developed using ANSYS mechanical APDL software program. The model was sectioned along the longitudinal section of a full interior flat slab. This reduces computational and disk storage demands. Simply support boundary condition was applied at flab slab bottom similar to experimental setup [11], and at a plane of symmetry along x-axis, the translation degree of freedom (DOF) in X-direction (Ux) is set to zero (Figure 6).Figure 6
Geometry, meshing, loading, and boundary conditions of part-II specimen.Thermal loading was applied on 1000 mm × 1000 mm area of the bottom of a flat slab. This area does not include support consistent with the experimental setup. The initial reference temperature was set to 20°C and then ISO-834 fire curve was gradually applied for 1-hour on flat slabs tension surface to simulate thermal loading. A displacement-controlled loading of 10 mm vertical displacement was applied at the top of a column to simulate gravity loading.


### 2.5. Finite Element Parametric Studies on Punching Shear Behavior of GFRP-ReinforcedSlab-Column Connection under Post-Earthquake Fire Loading

This section presents details of proposed finite element models and parameters to investigate punching shear of the GFRP-reinforcedslab-column connection subjected to post-earthquake fire. The parameters considered in the current study are effect of fire exposure duration, concrete grade, slab thickness, fire exposed surface, and column aspect ratio.Concrete mechanical properties such as compressive strength, tensile strength, and elastic modulus values were multiplied with reduction factors from Eurocode [19] to account for their degradation as a function of temperature. Similarly, reduction factors from Eurocode [19] were used to account for material strength loss as a function of temperature for yield strength and modulus of elasticity of the mechanical material properties of steel rebars. Moreover, ultimate strength and elastic modulus reduction factors of GFRP-reinforced bars were reproduced in [22], and the coefficient of thermal expansion material properties of GFRP bars is adopted from ACI 440.1R-15 [23]. Figures 7–19 present concrete and steel material characterizations at elevated temperatures.Figure 7
Concrete thermal conductivity [19].Figure 8
Concrete specific heat variation with temperature [19].Figure 9
Coefficient of thermal expansion [19].Figure 10
Concrete density variation with temperature [19].Figure 11
Concrete secant thermal expansion coefficient variation with temperatures [19].Figure 12
Concrete compressive strength reduction factor at elevated temperatures [19].Figure 13
Tensile strength reduction factor at elevated temperatures [19].Figure 14
Concrete modulus of elasticity variation with temperature [19].Figure 15
Thermal conductivity of steel at elevated temperatures [24].Figure 16
Volumetric specific heat for steel at elevated temperatures [24].Figure 17
Thermal elongation of steel at elevated temperature [19].A validated finite element model of the Part-I specimen was used for investigating the proposed parameters. However, additional thermal loading was applied to the bottom surface of flat slab to simulate post-earthquake fire loading. This thermal loading was applied to an area of 950 mm × 1900 mm, excluding support boundary conditions. Table4 presents a parametric study matrix table showing combination of variables and FEA runs to study the punching shear of the GFRP-reinforcedslab-column connection subjected to post-earthquake fire.Figure 18
Variation of secant thermal expansion coefficient with temperature [19].Figure 19
Variation of modulus of elasticity of reinforcement with temperature [19].Table 4
Parametric study matrix table of GFRP-reinforced slab-column connection with shear reinforcement under post-earthquake fire.
FE model IDSlab thickens (mm)Concrete grade (Mpa)Column aspect ratio (β)Fire exposure surfaceDuration of fire (minute)Effect of fire duration200-45-1-ALL Bs-40200451All bottom surface40200-45-1- ALL Bs-30200451All bottom surface30200-45-1- ALL Bs-20200451All bottom surface20200-45-1- ALL Bs-10200451All bottom surface10Effect of compressive strength of concrete200-35-1- ALL Bs-40200351All bottom surface40200-30-1- ALL Bs-40200301All bottom surface40200-25-1- ALL Bs-40200251All bottom surface40Effect of slab thickens150-45-1- ALL Bs-40150451All bottom surface40175-45-1- ALL Bs-40175451All bottom surface40250-45-1- ALL Bs-40250451All bottom surface40Effect of fire exposure side200-45-1- ALL Ts-40200451All top surface40200-45-1-Half Bs-40200451Half bottom surface40200-45-1-Half Ts-40200451Half top surface40Effect of aspect ratio200-45-1.16- ALL Bs-40200451.16All bottom surface40200-45-1.33- ALL Bs-40200451.33All bottom surface40200-45-1.66- ALL Bs-40200451.66All bottom surface40


### 2.6. Mesh Sensitivity Study

Employed element types, their mesh size, and aspect ratio affect the accuracy of finite element numerical simulation [25]. A finer mesh typically results in a more accurate solution; however, as high mesh density is used, computation time and disk storage increase exponentially [26]. Therefore, there is a need to choose a reasonable mesh size resulting in convergence of a solution by performing a mesh sensitivity study. In this study, the aspect ratio of brick element types was set to1, and FE mesh sensitivity study was executed with various element sizes ranging from 25 mm to 50 mm.Figure20 presents a comparison of experimental and FEA load deflection result plots for various mesh sizes. Mesh sensitivity FEA results showed a good agreement with experimental results both for Part-I and Part-II specimens. Optimizing FEA accuracy as compared to experimental results, total run time to complete analysis, and disk space usage, a mesh size of 50 mm and 25 mm was selected for subsequent FE parametric studies on Part-I and Part-II specimens.Figure 20
Mesh sensitivity study. (a) Effect of different mesh size for Part-I specimen. (b) Effect of different mesh size for Part-II specimen.
(a)(b)


## 2.1. Description of Part-I Specimen for FE Model Validation and Verification: GFRP-ReinforcedSlab-Column Connection under Lateral Cyclic Loading

Interior GFRP-reinforcedslab-column connection with GFRP shear reinforcement provided at 2 d from the face of a column, experimentally tested by [3] under reversed cyclic loading, was selected for validation and verification FEA of earthquake loading. This adequately designed GFRP-reinforcedslab-column connection specimen was also used as a control specimen.Experimental tests were conducted by [3] for shear-governedslab-column connections reinforced with glass fiber-reinforced polymer bars constructed without and with GFRP shear reinforcement. From these tested specimens, slab-column connections with GFR shear reinforcement were used to capture the effects of shear reinforcement as well as other investigated parameters for NLFEA. Also, from this shear reinforcement, provided slab-column connections used to provide shear reinforcement up to 2 d from the face of columns, this specimen is collapsed at 4.5% drifts, so we use this to capture the computational times of NLFEA compared to others shear reinforcement slab-column connection sample.


### 2.1.1. Details of Part-I Specimen

The geometry and reinforcement detailing characteristics of the developed FE model were identical to experimental work conducted by [3] on full-scaleGFRP-reinforcedslab-column connections with GFRP shear reinforcement provided at 2 d from the face of the column. The slab-column connection has a geometric dimension of 2500 mm × 2500 mm with a thickness of 200 mm and a 300 mm square column, extending 700 mm above and below slab surfaces (Figure 2). Sand-coated GFRP reinforcing bars (10 no. 15 and 14 no. 20) were used for flexural reinforcement at top and bottom of a slab, whereas closed GFRP shear reinforcement (16 no. 10) was also used in the slab. Moreover, six longitudinal deformed steel bars (25 M) and 16 closed ties (10 M) were used in columns. The reinforcement configurations of the specimen are shown in Figure 2 with bottom and top reinforcement placed symmetrically in each orthogonal direction.Figure 2
Geometry and reinforcement configuration of part-I slab-column connection specimen [3]. (a) Geometry (mm). (b) Reinforcement detailing.
(a)(b)


### 2.1.2. Material Properties of Part-I Specimen

Material properties employed for FE models were similar to experimental works conducted by [3] on full-scaleGFRP-reinforcedslab-column connections. Elastic module values of both bottom and top GFRP flexural reinforcements of a slab were 64.9 and 62.6 GPa, respectively, whereas elastic modulus of the GFRP shear reinforcement for the slab is 45 GPa. The yield strength of the main steel column rebar and steel column shear reinforcement was 4706 MPa and 2806 MPa, respectively. A compressive strength of concrete used for both slab and column was 45 MPa. Detailed material properties of concrete, GFRP, and steel rebar reinforcement are shown in Table 1.Table 1
Material properties of concrete, GFRP, and steel rebar reinforcement [3].
MaterialsConcretefc (MPa)fct (MPa)453.75Reinforcement typeBar sizeBar Փ (mm)Area (mm2)Elastic modulus (GPa)Ultimate tensile strength (MPa)Characteristics tensile strength (MPa)Ultimate tensile elongation (%)GFRP main slab barNo. 1515.919962.6123911841.89No. 2019.128564.9133410792.07Column steel bar25 M25.2490200Fu = 620Fy = 470εy = 0.24Steel stirrup10 M11.3100.2200—280—GFRP stirrupNo. 109.4971459485040.53


## 2.1.1. Details of Part-I Specimen

The geometry and reinforcement detailing characteristics of the developed FE model were identical to experimental work conducted by [3] on full-scaleGFRP-reinforcedslab-column connections with GFRP shear reinforcement provided at 2 d from the face of the column. The slab-column connection has a geometric dimension of 2500 mm × 2500 mm with a thickness of 200 mm and a 300 mm square column, extending 700 mm above and below slab surfaces (Figure 2). Sand-coated GFRP reinforcing bars (10 no. 15 and 14 no. 20) were used for flexural reinforcement at top and bottom of a slab, whereas closed GFRP shear reinforcement (16 no. 10) was also used in the slab. Moreover, six longitudinal deformed steel bars (25 M) and 16 closed ties (10 M) were used in columns. The reinforcement configurations of the specimen are shown in Figure 2 with bottom and top reinforcement placed symmetrically in each orthogonal direction.Figure 2
Geometry and reinforcement configuration of part-I slab-column connection specimen [3]. (a) Geometry (mm). (b) Reinforcement detailing.
(a)(b)


## 2.1.2. Material Properties of Part-I Specimen

Material properties employed for FE models were similar to experimental works conducted by [3] on full-scaleGFRP-reinforcedslab-column connections. Elastic module values of both bottom and top GFRP flexural reinforcements of a slab were 64.9 and 62.6 GPa, respectively, whereas elastic modulus of the GFRP shear reinforcement for the slab is 45 GPa. The yield strength of the main steel column rebar and steel column shear reinforcement was 4706 MPa and 2806 MPa, respectively. A compressive strength of concrete used for both slab and column was 45 MPa. Detailed material properties of concrete, GFRP, and steel rebar reinforcement are shown in Table 1.Table 1
Material properties of concrete, GFRP, and steel rebar reinforcement [3].
MaterialsConcretefc (MPa)fct (MPa)453.75Reinforcement typeBar sizeBar Փ (mm)Area (mm2)Elastic modulus (GPa)Ultimate tensile strength (MPa)Characteristics tensile strength (MPa)Ultimate tensile elongation (%)GFRP main slab barNo. 1515.919962.6123911841.89No. 2019.128564.9133410792.07Column steel bar25 M25.2490200Fu = 620Fy = 470εy = 0.24Steel stirrup10 M11.3100.2200—280—GFRP stirrupNo. 109.4971459485040.53


## 2.2. Finite Element Modeling of Part-I Specimen Using ANSYS Software Program

### 2.2.1. Element Types

CPT215 element type from ANSYS element library was used to model the concrete and steel loading plates. CPT215 element is a brick element with eight nodes and has three degrees of freedom per nodes. The element has the capability of stress stiffening, large deflection, elasticity, and large strain [12].Reinf264 element from ANSYS element library was employed to model steel and GFRP reinforcement. Reinf264 element is a uniaxial tension and compression element with two nodes. Reinf264 element has three translational degrees of freedom compatible with the parent concrete CPT 215 element [12]. This element is also capable of simulating nonlinearity and plastic deformations.


### 2.2.2. Material Types

A coupled damage-plasticity microplane model from ANSYS material library was used to model concrete material. A coupled damage-plasticity microplane model was formulated from research works of [13–15], where concrete material is characterized through uniaxial stress-strain laws of various individual planes [12].For the concrete, a coupled regularized damage-plasticity microplane model was used [13]. In this model, uniaxial stress vs. strain equations are applied to several small planes, referred to as microplanes, to approximate the material behavior. This method was used to capture the concrete’s inelastic behavior and get around the analysis’s numerical instability caused by the material’s strain softening [14]. A smooth, three-surface Drucker–Prager microplane with tension and compression cap surfaces serves as the definition for the coupled damage-plasticity microplane model. Limiting the yield surface’s expansion in both tension and compression is the fundamental benefit of using two cap surfaces.The use of a coupled damage-plasticity microplane model requires thirteen concrete material inputs out of which seven parameters are related to plasticity, four to damage, and two to nonlocal parameter. Parameters related to plasticity behavior of concrete includes Drucker–Prager yield function, compression cap, and hardening parameters [14, 15]. Drucker–Prager yield function parameters include listing of uniaxial compressive strength, biaxial compressive strength, and uniaxial tensile strength. The compression cap parameter listing refers to the abscissa intersection point between the compression cap and Drucker–Prager yield function and the ratio between the major and minor axes of the cap. Concrete plasticity hardening parameter listings are hardening material constant and tension cap hardening constant. The four damage parameter constants include tension and compression damage thresholds and tension and compression damage evolution constants. Last, two nonlocal parameters definition consisting of the nonlocal interaction range parameter and overnonlocal averaging parameter completes concrete material modeling using the coupled damage-plasticity microplane model. Table 2 presents details of concrete coupled damage-plasticity microplane model inputs for the Part-I FE model.Table 2
Concrete coupled damage-plasticity microplane model inputs.
ConstantValueE (MPa)36000Nu0.18C1 (MPa)45C2 (MPa)51.7C3 (MPa)3.8159C41C54000C6−31.5C72C80C90.00002C103000C112000C1600m2.5A bilinear isotropic and linear-elastic material model from ANSYS material library was used to characterize conventional steel rebars and GFRP reinforcement. Poisson’s ratios of 0.3 and 0.25 were employed for the steel and GFRP bars, respectively. Modulus of elasticity and Poisson’s ratio values of 200 GPa and 0.3 were used for steel loading plates material modeling. Table1 presents detailed material inputs of steel rebars, GFRP flexural bars, and shear stirrups. A perfect bond was assumed between the concrete and embedded rebar reinforcements.


### 2.2.3. Model Geometry, Boundary Conditions, and Loading

Taking advantage of the symmetry, half of GFRP-reinforcedslab-column connection subassemblage was modeled using ANSYS mechanical APDL. Half of the entire model was considered in the longitudinal section of full interior slab-column connection. This approach leads to a reduction in computational time and storage disk space requirement.A boundary condition was applied at the plane of symmetry and support locations to constrain nodes. At the plane of symmetry alongx-axis, translation degree of freedom (DOF) in X -direction (Ux) was set to zero, and at a support location similar to experimental set up [3], all translation DOF Ux, Uy, and Uz were set to zero. Moreover, identical to experimental set up [3], axial loading of 70 KN was applied at the top of a column to simulate gravity loading. Displacement-controlled FE analysis was performed by applying 60.75 mm of lateral displacement at a height of 675 mm from the center of a slab in the opposite direction on both top and bottom of columns. Figure 3 presents the loadings and boundary conditions of the developed FE model.Figure 3
Geometry, meshing, loading, and boundary conditions of part-I specimen.


## 2.2.1. Element Types

CPT215 element type from ANSYS element library was used to model the concrete and steel loading plates. CPT215 element is a brick element with eight nodes and has three degrees of freedom per nodes. The element has the capability of stress stiffening, large deflection, elasticity, and large strain [12].Reinf264 element from ANSYS element library was employed to model steel and GFRP reinforcement. Reinf264 element is a uniaxial tension and compression element with two nodes. Reinf264 element has three translational degrees of freedom compatible with the parent concrete CPT 215 element [12]. This element is also capable of simulating nonlinearity and plastic deformations.


## 2.2.2. Material Types

A coupled damage-plasticity microplane model from ANSYS material library was used to model concrete material. A coupled damage-plasticity microplane model was formulated from research works of [13–15], where concrete material is characterized through uniaxial stress-strain laws of various individual planes [12].For the concrete, a coupled regularized damage-plasticity microplane model was used [13]. In this model, uniaxial stress vs. strain equations are applied to several small planes, referred to as microplanes, to approximate the material behavior. This method was used to capture the concrete’s inelastic behavior and get around the analysis’s numerical instability caused by the material’s strain softening [14]. A smooth, three-surface Drucker–Prager microplane with tension and compression cap surfaces serves as the definition for the coupled damage-plasticity microplane model. Limiting the yield surface’s expansion in both tension and compression is the fundamental benefit of using two cap surfaces.The use of a coupled damage-plasticity microplane model requires thirteen concrete material inputs out of which seven parameters are related to plasticity, four to damage, and two to nonlocal parameter. Parameters related to plasticity behavior of concrete includes Drucker–Prager yield function, compression cap, and hardening parameters [14, 15]. Drucker–Prager yield function parameters include listing of uniaxial compressive strength, biaxial compressive strength, and uniaxial tensile strength. The compression cap parameter listing refers to the abscissa intersection point between the compression cap and Drucker–Prager yield function and the ratio between the major and minor axes of the cap. Concrete plasticity hardening parameter listings are hardening material constant and tension cap hardening constant. The four damage parameter constants include tension and compression damage thresholds and tension and compression damage evolution constants. Last, two nonlocal parameters definition consisting of the nonlocal interaction range parameter and overnonlocal averaging parameter completes concrete material modeling using the coupled damage-plasticity microplane model. Table 2 presents details of concrete coupled damage-plasticity microplane model inputs for the Part-I FE model.Table 2
Concrete coupled damage-plasticity microplane model inputs.
ConstantValueE (MPa)36000Nu0.18C1 (MPa)45C2 (MPa)51.7C3 (MPa)3.8159C41C54000C6−31.5C72C80C90.00002C103000C112000C1600m2.5A bilinear isotropic and linear-elastic material model from ANSYS material library was used to characterize conventional steel rebars and GFRP reinforcement. Poisson’s ratios of 0.3 and 0.25 were employed for the steel and GFRP bars, respectively. Modulus of elasticity and Poisson’s ratio values of 200 GPa and 0.3 were used for steel loading plates material modeling. Table1 presents detailed material inputs of steel rebars, GFRP flexural bars, and shear stirrups. A perfect bond was assumed between the concrete and embedded rebar reinforcements.


## 2.2.3. Model Geometry, Boundary Conditions, and Loading

Taking advantage of the symmetry, half of GFRP-reinforcedslab-column connection subassemblage was modeled using ANSYS mechanical APDL. Half of the entire model was considered in the longitudinal section of full interior slab-column connection. This approach leads to a reduction in computational time and storage disk space requirement.A boundary condition was applied at the plane of symmetry and support locations to constrain nodes. At the plane of symmetry alongx-axis, translation degree of freedom (DOF) in X -direction (Ux) was set to zero, and at a support location similar to experimental set up [3], all translation DOF Ux, Uy, and Uz were set to zero. Moreover, identical to experimental set up [3], axial loading of 70 KN was applied at the top of a column to simulate gravity loading. Displacement-controlled FE analysis was performed by applying 60.75 mm of lateral displacement at a height of 675 mm from the center of a slab in the opposite direction on both top and bottom of columns. Figure 3 presents the loadings and boundary conditions of the developed FE model.Figure 3
Geometry, meshing, loading, and boundary conditions of part-I specimen.


## 2.3. Description of Part-II Specimen for FE Model Validation and Verification: Punching Shear Strength of Reinforced Concrete Flat Slab Subjected to Fire Loading

In this section, experimental data reported by [11] on punching shear strength of reinforced concrete flat slab subjected to fire on their tension was chosen for validation and verification FEA of fire loading. This Part-II FE validation analysis complements the Part-I FE model validation on the application of fire loading. Details of the specimen are presented in the next few subsections.


### 2.3.1. Detailing of the Specimen

A full-scale RC flat slab specimen chosen for FE validation analysis on fire loading has width and length geometric dimensions of 1100 × 1100 mm. The flat slab has 100 mm thickness and a 150 mm square column extending 400 mm height above the flat slab surface. The flat slab was reinforced with 11 Φ 10 mm rebars in the tension side and 7 Φ 10 mm in the compression side. Similarly, the column was detailed with 4 Φ 10 longitudinal rebars and 4 Φ 8 mm stirrups. Figure4 shows rebar detailing of Part-II specimen.Figure 4
Reinforcement detailing of part-II specimen [11]. (a) Compression reinforcement. (b) Tension reinforcement. (c) Center line section.
(a)(b)(c)


### 2.3.2. Material Properties of Part-II Specimen

RC flat slab Part-II specimen was reinforced with 10 mm diameter deformed rebars, whereas column stirrups were made of 8 mm diameter plain rebars. The deformed and plain bars had yield stresses of 410 and 270 MPa, respectively. The flat slab had concrete compressive strength of 25 MPa. Table3 shows details of flat slab concrete and rebar material properties.Table 3
Material properties of concrete and reinforcement [11].
MaterialsConcreteCompressive strength, fc (MPa)25ReinforcementBar sizeBar diam. (mm)Elastic tensile modulus (GPa)Yield strength in (MPa)Steel main barΦ1010200410Steel stirrupΦ88200270


## 2.3.1. Detailing of the Specimen

A full-scale RC flat slab specimen chosen for FE validation analysis on fire loading has width and length geometric dimensions of 1100 × 1100 mm. The flat slab has 100 mm thickness and a 150 mm square column extending 400 mm height above the flat slab surface. The flat slab was reinforced with 11 Φ 10 mm rebars in the tension side and 7 Φ 10 mm in the compression side. Similarly, the column was detailed with 4 Φ 10 longitudinal rebars and 4 Φ 8 mm stirrups. Figure4 shows rebar detailing of Part-II specimen.Figure 4
Reinforcement detailing of part-II specimen [11]. (a) Compression reinforcement. (b) Tension reinforcement. (c) Center line section.
(a)(b)(c)


## 2.3.2. Material Properties of Part-II Specimen

RC flat slab Part-II specimen was reinforced with 10 mm diameter deformed rebars, whereas column stirrups were made of 8 mm diameter plain rebars. The deformed and plain bars had yield stresses of 410 and 270 MPa, respectively. The flat slab had concrete compressive strength of 25 MPa. Table3 shows details of flat slab concrete and rebar material properties.Table 3
Material properties of concrete and reinforcement [11].
MaterialsConcreteCompressive strength, fc (MPa)25ReinforcementBar sizeBar diam. (mm)Elastic tensile modulus (GPa)Yield strength in (MPa)Steel main barΦ1010200410Steel stirrupΦ88200270


## 2.4. Finite Element Modeling of Part-II Specimen Using ANSYS Software Program

A sequential coupled-field analysis was performed to simulate fire loading using ANSYS software program. First, heat transfer thermal analysis is performed followed by coupled structural analysis. Briefly, temperatures at each node of a FE model are evaluated from thermal analysis and used as input data in following structural analysis. Finally, structural evaluations are performed to determine the structural collapse that occurs when a structure is exposed to both fire and applied forces [16].


### 2.4.1. Fire Loading

In the present study, applied fire loading was characterized using fire loading curve from the international standardization organization (ISO834) [17]. The fire loading curve (Figure 5) is characterized using the following equation:(1)T=345log8t+1+20,where T indicates temperature, in degrees celsius, and t indicates time, in minutes.Figure 5
ISO-834 fire curve [17].


### 2.4.2. Sequential Coupled-Field Finite Element Analysis

Heat transfer is a measure of thermal load which simulates fire loading. The amount of heat transferred through a body is referred to as heat transfer. When temperatures of two systems differ, heat is transferred from a higher temperature to a lower temperature, eventually forming the two systems back into equilibrium through conduction, convection, or radiation mechanism [18].Transient thermal analysis where material properties change over time as a function of temperature was executed to simulate fire loading. Transient thermal analysis requires inputs such as density, thermal conductivity, and specific heat of a material. Aforementioned material inputs were entered as a function of temperature using reduction factors from [19].In multiphysics simulations, ANSYS software program performs finite element numerical analysis of reinforced concrete slabs subjected to fire in two steps: first, transient thermal analysis is performed, followed by coupled structural analysis [12, 20].Element types, SOLID70 and SURF152, from ANSYS element library were used to model concrete and target fire loading surface area in transient thermal FE analyses, respectively. Eurocode [19] was used to define the thermal material properties of concrete. Applying sequential coupled-field analysis technique requires first transient thermal analysis to be completed, and this is followed up performing structural analysis using nodal temperature results from former analysis as an input to latter FE structural analysis [12, 21]. However, FE model and geometry must remain the same in both analysis types.Perfect bond was assumed between concrete and GFRP rebars. This assumption implies that GFRP rebar nodes in a FE model have identical nodal temperature value with parent concrete element.In sequential coupled-field analysis, four procedures need to be executed while moving from thermal analysis to coupled structural analysis. First, thermal element types are switched with equivalent structural elements. In this study, thermal element SOLID70 was swapped with SOLID185 and CPT 215 structural elements [12]. Second, concrete and steel rebar mechanical are input as a function of temperature. In the present article, reduction factors from Eurocode [19] were employed to define concrete and steel rebar material properties as a function of temperature. Third, SURF152 elements are deleted from the FE model. SURF152 element was used to define target fire exposed external flat slab concrete surfaces in thermal analysis, and they are no longer required in a follow up coupled structural analysis.Finally, in fourth step, boundary conditions and structural load are applied before performing coupled structural FEA. In this study, boundary conditions were applied at plane of symmetry (UX = 0) and support locations (Ux, Uy, and Uz = 0) to constrain respective nodal translation degrees of freedom. Next, structural lateral and axial loads were applied, and coupled structural analysis was performed to learn the punching shear behavior of GFRP-reinforcedslab-column connection subjected to post-earthquake fire loading.


### 2.4.3. Geometry, Boundary Conditions, and Loading

Taking advantage of symmetry, a half-full model according to experimental details [11] was developed using ANSYS mechanical APDL software program. The model was sectioned along the longitudinal section of a full interior flat slab. This reduces computational and disk storage demands. Simply support boundary condition was applied at flab slab bottom similar to experimental setup [11], and at a plane of symmetry along x-axis, the translation degree of freedom (DOF) in X-direction (Ux) is set to zero (Figure 6).Figure 6
Geometry, meshing, loading, and boundary conditions of part-II specimen.Thermal loading was applied on 1000 mm × 1000 mm area of the bottom of a flat slab. This area does not include support consistent with the experimental setup. The initial reference temperature was set to 20°C and then ISO-834 fire curve was gradually applied for 1-hour on flat slabs tension surface to simulate thermal loading. A displacement-controlled loading of 10 mm vertical displacement was applied at the top of a column to simulate gravity loading.


## 2.4.1. Fire Loading

In the present study, applied fire loading was characterized using fire loading curve from the international standardization organization (ISO834) [17]. The fire loading curve (Figure 5) is characterized using the following equation:(1)T=345log8t+1+20,where T indicates temperature, in degrees celsius, and t indicates time, in minutes.Figure 5
ISO-834 fire curve [17].


## 2.4.2. Sequential Coupled-Field Finite Element Analysis

Heat transfer is a measure of thermal load which simulates fire loading. The amount of heat transferred through a body is referred to as heat transfer. When temperatures of two systems differ, heat is transferred from a higher temperature to a lower temperature, eventually forming the two systems back into equilibrium through conduction, convection, or radiation mechanism [18].Transient thermal analysis where material properties change over time as a function of temperature was executed to simulate fire loading. Transient thermal analysis requires inputs such as density, thermal conductivity, and specific heat of a material. Aforementioned material inputs were entered as a function of temperature using reduction factors from [19].In multiphysics simulations, ANSYS software program performs finite element numerical analysis of reinforced concrete slabs subjected to fire in two steps: first, transient thermal analysis is performed, followed by coupled structural analysis [12, 20].Element types, SOLID70 and SURF152, from ANSYS element library were used to model concrete and target fire loading surface area in transient thermal FE analyses, respectively. Eurocode [19] was used to define the thermal material properties of concrete. Applying sequential coupled-field analysis technique requires first transient thermal analysis to be completed, and this is followed up performing structural analysis using nodal temperature results from former analysis as an input to latter FE structural analysis [12, 21]. However, FE model and geometry must remain the same in both analysis types.Perfect bond was assumed between concrete and GFRP rebars. This assumption implies that GFRP rebar nodes in a FE model have identical nodal temperature value with parent concrete element.In sequential coupled-field analysis, four procedures need to be executed while moving from thermal analysis to coupled structural analysis. First, thermal element types are switched with equivalent structural elements. In this study, thermal element SOLID70 was swapped with SOLID185 and CPT 215 structural elements [12]. Second, concrete and steel rebar mechanical are input as a function of temperature. In the present article, reduction factors from Eurocode [19] were employed to define concrete and steel rebar material properties as a function of temperature. Third, SURF152 elements are deleted from the FE model. SURF152 element was used to define target fire exposed external flat slab concrete surfaces in thermal analysis, and they are no longer required in a follow up coupled structural analysis.Finally, in fourth step, boundary conditions and structural load are applied before performing coupled structural FEA. In this study, boundary conditions were applied at plane of symmetry (UX = 0) and support locations (Ux, Uy, and Uz = 0) to constrain respective nodal translation degrees of freedom. Next, structural lateral and axial loads were applied, and coupled structural analysis was performed to learn the punching shear behavior of GFRP-reinforcedslab-column connection subjected to post-earthquake fire loading.


## 2.4.3. Geometry, Boundary Conditions, and Loading

Taking advantage of symmetry, a half-full model according to experimental details [11] was developed using ANSYS mechanical APDL software program. The model was sectioned along the longitudinal section of a full interior flat slab. This reduces computational and disk storage demands. Simply support boundary condition was applied at flab slab bottom similar to experimental setup [11], and at a plane of symmetry along x-axis, the translation degree of freedom (DOF) in X-direction (Ux) is set to zero (Figure 6).Figure 6
Geometry, meshing, loading, and boundary conditions of part-II specimen.Thermal loading was applied on 1000 mm × 1000 mm area of the bottom of a flat slab. This area does not include support consistent with the experimental setup. The initial reference temperature was set to 20°C and then ISO-834 fire curve was gradually applied for 1-hour on flat slabs tension surface to simulate thermal loading. A displacement-controlled loading of 10 mm vertical displacement was applied at the top of a column to simulate gravity loading.


## 2.5. Finite Element Parametric Studies on Punching Shear Behavior of GFRP-ReinforcedSlab-Column Connection under Post-Earthquake Fire Loading

This section presents details of proposed finite element models and parameters to investigate punching shear of the GFRP-reinforcedslab-column connection subjected to post-earthquake fire. The parameters considered in the current study are effect of fire exposure duration, concrete grade, slab thickness, fire exposed surface, and column aspect ratio.Concrete mechanical properties such as compressive strength, tensile strength, and elastic modulus values were multiplied with reduction factors from Eurocode [19] to account for their degradation as a function of temperature. Similarly, reduction factors from Eurocode [19] were used to account for material strength loss as a function of temperature for yield strength and modulus of elasticity of the mechanical material properties of steel rebars. Moreover, ultimate strength and elastic modulus reduction factors of GFRP-reinforced bars were reproduced in [22], and the coefficient of thermal expansion material properties of GFRP bars is adopted from ACI 440.1R-15 [23]. Figures 7–19 present concrete and steel material characterizations at elevated temperatures.Figure 7
Concrete thermal conductivity [19].Figure 8
Concrete specific heat variation with temperature [19].Figure 9
Coefficient of thermal expansion [19].Figure 10
Concrete density variation with temperature [19].Figure 11
Concrete secant thermal expansion coefficient variation with temperatures [19].Figure 12
Concrete compressive strength reduction factor at elevated temperatures [19].Figure 13
Tensile strength reduction factor at elevated temperatures [19].Figure 14
Concrete modulus of elasticity variation with temperature [19].Figure 15
Thermal conductivity of steel at elevated temperatures [24].Figure 16
Volumetric specific heat for steel at elevated temperatures [24].Figure 17
Thermal elongation of steel at elevated temperature [19].A validated finite element model of the Part-I specimen was used for investigating the proposed parameters. However, additional thermal loading was applied to the bottom surface of flat slab to simulate post-earthquake fire loading. This thermal loading was applied to an area of 950 mm × 1900 mm, excluding support boundary conditions. Table4 presents a parametric study matrix table showing combination of variables and FEA runs to study the punching shear of the GFRP-reinforcedslab-column connection subjected to post-earthquake fire.Figure 18
Variation of secant thermal expansion coefficient with temperature [19].Figure 19
Variation of modulus of elasticity of reinforcement with temperature [19].Table 4
Parametric study matrix table of GFRP-reinforced slab-column connection with shear reinforcement under post-earthquake fire.
FE model IDSlab thickens (mm)Concrete grade (Mpa)Column aspect ratio (β)Fire exposure surfaceDuration of fire (minute)Effect of fire duration200-45-1-ALL Bs-40200451All bottom surface40200-45-1- ALL Bs-30200451All bottom surface30200-45-1- ALL Bs-20200451All bottom surface20200-45-1- ALL Bs-10200451All bottom surface10Effect of compressive strength of concrete200-35-1- ALL Bs-40200351All bottom surface40200-30-1- ALL Bs-40200301All bottom surface40200-25-1- ALL Bs-40200251All bottom surface40Effect of slab thickens150-45-1- ALL Bs-40150451All bottom surface40175-45-1- ALL Bs-40175451All bottom surface40250-45-1- ALL Bs-40250451All bottom surface40Effect of fire exposure side200-45-1- ALL Ts-40200451All top surface40200-45-1-Half Bs-40200451Half bottom surface40200-45-1-Half Ts-40200451Half top surface40Effect of aspect ratio200-45-1.16- ALL Bs-40200451.16All bottom surface40200-45-1.33- ALL Bs-40200451.33All bottom surface40200-45-1.66- ALL Bs-40200451.66All bottom surface40


## 2.6. Mesh Sensitivity Study

Employed element types, their mesh size, and aspect ratio affect the accuracy of finite element numerical simulation [25]. A finer mesh typically results in a more accurate solution; however, as high mesh density is used, computation time and disk storage increase exponentially [26]. Therefore, there is a need to choose a reasonable mesh size resulting in convergence of a solution by performing a mesh sensitivity study. In this study, the aspect ratio of brick element types was set to1, and FE mesh sensitivity study was executed with various element sizes ranging from 25 mm to 50 mm.Figure20 presents a comparison of experimental and FEA load deflection result plots for various mesh sizes. Mesh sensitivity FEA results showed a good agreement with experimental results both for Part-I and Part-II specimens. Optimizing FEA accuracy as compared to experimental results, total run time to complete analysis, and disk space usage, a mesh size of 50 mm and 25 mm was selected for subsequent FE parametric studies on Part-I and Part-II specimens.Figure 20
Mesh sensitivity study. (a) Effect of different mesh size for Part-I specimen. (b) Effect of different mesh size for Part-II specimen.
(a)(b)


## 3. Results and Discussion

This section describes the findings of validated and parametric FEA results. The main parameters investigated in this study include effects of post-earthquake fire exposure duration, concrete grade, slab thickness, fire exposed surface, and column aspect ratio on punching performance of GFRP-reinforcedslab-column connections. Moreover, comparisons of FE validation analysis results and two experimental tests of two interior slab-column connections [3, 11] are presented.


### 3.1. FE Validation Analysis Results

Finite element studies and their comparison with the experimental test results for verification are extremely important in order to idealize the real behavior of the tested specimens and predict the behavior of other specimens that cannot be tested experimentally. This verification could provide evidence about the applicability of the finite element model to investigate structural behavior. In this study, two experimental tests from the article [3, 11] on GFRP-reinforcedslab-column connection with GFRP shear reinforcement provided at 2 d from the face of the column were used for FE validation analysis.The accuracy of the nonlinear finite element model was evaluated by comparing the NLFEA results of these two specimens with the experimental result in terms of unbalanced moment drift ratio and failure pattern for model G6CS–2d tested by [3] and also for model S1 tested by [11], in terms of load-displacement response and failure pattern.


#### 3.1.1. Unbalanced Moment Drift Ratio for G6CS-2d Specimen and Load-Displacement for S1 Specimen Response

(1) GFRP-ReinforcedSlab-Column Connection Specimen, G6CS-2d. Figure 21 shows comparison of the unbalanced moment drift ratio response obtained from NLFEA compared with the experimental results of the specimen G6CS-2d.Figure 21
Unbalanced moment drift ratio graph for G6CS-2d specimen.The NLFEA’s unbalanced moment drift ratio response of the specimen GFRP-reinforcedslab-column connection (G6CS-2d) is a good agreement with the experimental result. The maximum unbalanced moment obtained from the NLFEA of this specimen is 1.32% lower than the maximum unbalanced moment reported from the experimental study (see Table5). The higher stiffness observed in NLFEA results as compared to the experimental results might be due to the formation of microcracks in the experimental test, thus reducing its stiffness, whereas in finite element models do not fully capture the development of these microcracks [27]. Also, the perfect bond assumption between concrete and reinforcement in developed finite element models might account for the aforementioned minor differences between NLFEA and experimental results.Table 5
Maximum unbalanced moment and maximum load comparisons of NLFEA prediction with the test results of the two specimens.
SpecimenMaximum lateral load (kN)Maximum unbalanced moment (KN.m)Specimen 1 ID nameNLFEATestError (%)NLFEATestError (%)G6CS–2d148.68150.9−1.47195.985198.6−1.32SpecimenMaximum axial load (KN)PredictionSpecimen 2 ID nameNLFEATestError (%)S1185.211793.47(2) Reinforced Concrete Flat Slab Specimen, S1. As can be seen in Figure 22, the load-displacement curves of NLFEA and experimental results showed good agreement. The maximum load obtained from NLFEA analysis was 3.47% higher than the maximum load reported from the experimental study (see Table 5). Table 5 shows accuracy of NLFEA results for the two specimens as compared with the experimental test results. It describes the overall model accuracy of the NLFEA. The error (%) was evaluated based on the relation given in [28] and as shown in the following:(2)error%=NLFEA−testresulttestresult∗100.Figure 22
Load-displacement curve for specimen S1.In all cases, the FEA results of the connection punching shear cracking, unbalanced moment, and maximum load fall to an error of less than 5% implying that the finite element response of the specimens is in good agreement with experimental test results. This indicates that employed material properties and constitutive models were capable of capturing the response of GFRP-reinforcedslab-column connection with GFRP shear reinforcement.


#### 3.1.2. Failure Patternsald

(1) GFRP-ReinforcedSlab-Column Connection Specimen, G6CS-2d. Figure 23 shows side by side comparison of crack patterns of NLFEA and experimental test results at failure load for specimens G6CS-2d.Figure 23
Comparison of concrete damage of specimen G6CS-2d at failure load. (a) Experimental half-scale [8]. (b) FEA half-scale plan view. (c) FEA half-scale 3D view.
(a)(b)(c)Figure23 shows that the numerical model shows good agreement between the punching shear cracking pattern obtained from NLFEA and the punching shear crack propagation pattern reported in the experimental study. In both results, punching cracking patterns concentrated on GFRP-reinforcedslab-column connection.(2) Reinforced Concrete Flat Slab Specimen, S1. Figure 24 presents FEA temperature distributions of flat slab specimen, S1 after 3600sec fire exposure, whereas Figure 25 shows the comparison of crack patterns in specimens S1 between NLFEA and experimental test results at the failure load stage.Figure 24
FEA temperature distributions after 3600 sec fire exposure at the bottom of specimen S1 slab.Figure 25
Comparison of concrete damage of specimen S1 due to 3600 sec fire exposure and maximum load. (a) Experimental half-scale [11]. (b) FEA half-scale plan view. (c) FEA half-scale 3D view.
(a)(b)(c)Overall failure patterns as predicted by NLFEA showed good agreement with experimental test results. Therefore, developed FE models can be used as an effective and reliable tool to study effect of various influential parameters on post-earthquake fire punching shear behavior of GFRP-reinforcedslab-column connections.Aforementioned validated FE model was used as a controlling specimen of GFRP-reinforcedslab-column connection with GFRP shear reinforcement provided at 2d from the face of the column under an earthquake and axial load at ambient temperature. Then, in subsequent parametric studies, the validated FE model was subjected to post-earthquake fire at the bottom surface of the slab besides to lateral load and 0%, 10%, 20%, and 50% axial loading levels. Nevertheless, except for the aforementioned applied loads, the control specimen’s detailing had been kept identical to the experimental test in [3]. FEA results such as unbalanced moment drift ratio and drift ratio-fire duration response for an all-varied axial load level loading are discussed below.Figures26–29 show the effect of varied axial load levels on the unbalanced moment drift ratio and drift ratio-fire duration response. FEA results showed that changes in axial loading levels affected slab-column connection fire resistance performance. As the axial load ratio increased from 0% to 10% to 20% and 50%, slab-column connection fire resistance reduced to 49.87 min, 25.48 min, 5.48 min, and 4.65 min, respectively. For subsequent parametric studies, a FE model with 0% axial load level, 3.07% drift ratio, and 40 min post-earthquake fire exposure duration was used as a control specimen. Next, Figures 30–33 present nodal temperature distribution, unbalanced moment drift ratio, homogenized concrete damage, and rebar strain for a 0% axial load level control specimen.Figure 26
(a) Unbalanced moment drift ratio response and (b) drift ratio-fire exposed duration response of 0% axial load level.
(a)(b)Figure 27
(a) Unbalanced moment drift ratio response and (b) drift ratio-fire exposed duration response of 10% axial load level.
(a)(b)Figure 28
(a) Unbalanced moment drift ratio response and (b) drift ratio-fire exposed duration response of 20% axial load level.
(a)(b)Figure 29
(a) Unbalanced moment drift ratio response and (b) drift ratio-fire exposed duration response of 50% axial load level.
(a)(b)Figure 30
Nodal temperature distribution of control specimen with 2400 sec fire exposure at the bottom surface of slab. (a) 3D view of nodal temperature distribution of the control specimen. (b) Centerline section view of nodal temperature distribution of the control specimen.
(a)(b)Figure 31
The control specimen’s time versus temperature behavior during a 2400 sec fire exposure at the bottom surface of a slab at varying slab depths.Figure 32
Control specimen’s unbalanced moment drift ratio response with 2400 sec fire exposure.Figure 33
Total concrete damage to control specimen due to 2400 sec fire exposure at the bottom of the slab. (a) Total concrete damage at maximum load. (b) Bottom surface total concrete damage at maximum load. (c) Total concrete damage at failure load. (d) Bottom surface total concrete damage at failure load.
(a)(b)(c)(d)


### 3.2. FEA Parametric Studies on GFRP-ReinforcedSlab-Column Connections with GFRP Shear Reinforcement Subjected to Post-Earthquake Fire

This section presents the response of GFRP-reinforcedslab-column connections with GFRP shear reinforcement provided at 2d from the face of the column under post-earthquake fire loading. Effects of influential parameters such as fire exposure duration, concrete grade, slab thickness, fire exposed surface, and column aspect ratio are investigated thoroughly.


#### 3.2.1. Effect of Post-Earthquake Fire Exposure Duration

Three different fire exposure durations of 600, 1200, and 1800 seconds were selected and applied to study the impact of fire exposure duration on GFRP-reinforcedslab-column connections under post-earthquake fire loading. Next, the unbalanced moment drift ratio and concrete damage results of these specimens are examined in contrast to the control specimen.FEA results of GFRP-reinforcedslab-column connections under post-earthquake fire exposure for durations of 1800, 1200, and 600 seconds exhibited maximum unbalanced moment of 174.60 KN·m, 179.28 KN·m, and 187.77 KN·m, respectively (Figure34). A decrease in post-earthquake fire exposure duration from 2400 to 600 seconds resulted in peak of unbalanced moment drift ratio in slab-column connections in ranges of 1.89% to 9.58%. This implies higher post-earthquake fire exposure results in increase in temperature distribution of a specimen leading to deterioration of concrete and reinforcement material properties.Figure 34
Effect of post-earthquake fire exposure duration on unbalanced moment drift ratio response.Figure35 presents the nodal temperature distribution for various post-earthquake fire duration and as post-earthquake fire duration increased, so does concrete damages in respective specimens.Figure 35
Concrete damage of specimens with varying post-earthquake fire exposure durations. (a) Specimen 200-45-1-ALL Bs-1800. (b) Bottom surface. (c) Specimen 200-45-1-ALL Bs-1200. (d) Bottom surface. (e) Specimen 200-45-1-ALL Bs-600. (f) Bottom surface.
(a)(b)(c)(d)(e)(f)


#### 3.2.2. Effect of Concrete Grade

Analytical formulas in ACI and Eurocode codes of practice use compressive strength of concrete as a key parameter to evaluate punching shear stress of concrete slab. The control specimen has C-45 MPa concrete grade, and the current parametric study on grade of concrete three different concrete grades was considered, namely, C-25 MPa, C-30 MPa, and C-35 MPa.Figure36 shows that the increasing concrete grade leads to an increase in punching shear capacity. Maximum unbalanced moment of 125.48 KN·m, 138.60 KN·m, and 150.48 KN·m was recorded for GFRP-reinforcedslab-column connections with concrete grades of C-25, C-30, and C-35, respectively, and as compared to control, the losses were −26.77%,−19.11%, and −12.18%. Raising concrete grade has shown better punching shear carrying capacity of GFRP-reinforcedslab-column connections subjected to post-earthquake fire.Figure 36
Effect of concrete grade on unbalanced moment drift ratio.Figure37 shows FEA concrete damage results of GFRP-reinforcedslab-column connections subjected to post-earthquake fire for concrete grades C-25, C-30, and C-35. The results imply that concrete grade has minor effect on lessening concrete damage.Figure 37
Concrete damage of specimens with varying concrete grade. (a) Specimen 200-25-1-ALL Bs-2400. (b) Bottom surface. (c) Specimen 200-30-1-ALL Bs-2400. (d) Bottom surface. (e) Specimen 200-35-1-ALL Bs-2400. (f) Bottom surface.
(a)(b)(c)(d)(e)(f)


#### 3.2.3. Effect of Slab Thickness

Three different slab thicknesses of 150 mm, 175 mm, and 250 mm were selected to study effect of slab thickness on behavior of GFRP-reinforcedslab-column connections subjected to post-earthquake fire. FEA results showed thickness of the slab affected structural performance of GFRP-reinforcedslab-column connections subjected to post-earthquake fire.FEA results for slab thicknesses of 150 mm, 175 mm, and 250 mm displayed ultimate moment of 133.24 KN·m, 162.34 KN·m, and 210.50 KN·m (Figure38), and as compared to control, variations were −22.24%, −5.26%, and 22.85%. Increasing slab thickness decreased heat transfer across slab section resulting minor concrete deterioration. Moreover, increasing slab thickness enlarged effective depth of the specimens which in turn raised shear resistance of concrete due to aggregate interlocking.Figure 38
Effect of slab thickens on unbalanced moment drift ratio.Figure39 presents the nodal temperature variations for GFRP-reinforcedslab-column connections with slab thicknesses of 150 mm, 175 mm, and 250 mm. As slab thickness increased, the nodal temperature variations across slab thickness were reduced.Figure 39
Concrete damage of specimens with varying slab thickness. (a) Specimen 150-45-1-ALL Bs-2400. (b) Bottom surface. (c) Specimen 175-45-1-ALL Bs-2400. (d) Bottom surface. (e) Specimen 250-45-1-ALL Bs-2400. (f) Bottom surface.
(a)(b)(c)(d)(e)(f)


#### 3.2.4. Effect of Fire Exposed Surface

Three varied surface areas such as all top slab surface, half top slab surface, and half bottom slab surface were selected, and post-earthquake fire loading was applied on aforementioned proposed exposed surfaces of slab to study impact of exposed surface on post-earthquake fire behavior of GFRP-reinforcedslab-column connection.FEA results indicated that as compared to control, maximum unbalanced moment peaked by 7.73%, 14.18%, and 14.29% for specimens with post-earthquake fire exposed surfaces of all top slab surface, half top slab surface, and half bottom slab, respectively. Also, results show that post-earthquake fire exposed to the bottom surface exhibits a higher punching strength structural performance loss than the other two (Figure40).Figure 40
Effect of post-earthquake fire exposed surfaces on unbalanced moment drift ratio.Figure41 presents concrete damage for various post-earthquake fire exposed surfaces. Top surface of slab fire exposure exhibited higher concrete damage than the bottom surface of slab fire exposure. This can be accounted to the lower top reinforcement ratio as compared to the bottom GFRP-reinforcedslab-column connection.Figure 41
Concrete damage of specimens with varying fire exposed surface. (a) Specimen 200-45-1-ALL TS-2400. (b) Bottom surface. (c) Specimen 200-45-1-Half TS-2400. (d) Bottom surface. (e) Specimen 200-45-1-Half BS-2400. (f) Bottom surface.
(a)(b)(c)(d)(e)(f)


#### 3.2.5. Effect of Column Rectangularity (Aspect Ratio)

The column aspect ratio, or rectangularity, is calculated by the ratio of lengths of long and short sides of a column. Column rectangularity would have an impact on the punching capacity of flat plates by reducing the shear stress capacity along the critical perimeter. This hypothesis was tested by considering three different column rectangularity indexes (β = 1.16, 1.33, and 1.66) on GFRP-reinforcedslab-column connection under post-earthquake fire loading.FEA results showed that as compared to control (β = 1), GFRP-reinforcedslab-column connection with column aspect ratios of 300 × 350 mm (β = 1.16), 300 × 400 mm (β = 1.33), and 300 × 500 mm (β = 1.66) exhibited ultimate moments increments of 21.41%, 51.53%, and 99.21%, respectively (Figure 42). Increasing column aspect ratio decreased shear stress capacity along the critical perimeter and pushed failure perimeters away from the column.Figure 42
Effect of column aspect ratio on unbalanced moment drift ratio.Figure43 presents concrete damages for GFRP-reinforcedslab-column connection models under post-earthquake fire with various column aspect ratio. Column aspect ratio increment has illustrated a higher effect on decreasing concrete damage relative to gains in unbalanced moment drift ratios. This is attributed to column aspect ratio increments lead failure perimeters away from the column, which indirectly lessens concrete damage. However, at an aspect ratio of 1.66, concrete damage increased as compared to others. This can be accounted to the formation of stress concentration at the corner location of the column.Figure 43
Concrete damage of specimens with varying column aspect ratio. (a) Specimen 200-45-1.166-ALL BS-2400. (b) Bottom surface. (c) Specimen 200-45-1.333-ALL BS-2400. (d) Bottom surface. (e) Specimen 200-45-1.666-ALL BS-2400. (f) Bottom surface.
(a)(b)(c)(d)(e)(f)


## 3.1. FE Validation Analysis Results

Finite element studies and their comparison with the experimental test results for verification are extremely important in order to idealize the real behavior of the tested specimens and predict the behavior of other specimens that cannot be tested experimentally. This verification could provide evidence about the applicability of the finite element model to investigate structural behavior. In this study, two experimental tests from the article [3, 11] on GFRP-reinforcedslab-column connection with GFRP shear reinforcement provided at 2 d from the face of the column were used for FE validation analysis.The accuracy of the nonlinear finite element model was evaluated by comparing the NLFEA results of these two specimens with the experimental result in terms of unbalanced moment drift ratio and failure pattern for model G6CS–2d tested by [3] and also for model S1 tested by [11], in terms of load-displacement response and failure pattern.


### 3.1.1. Unbalanced Moment Drift Ratio for G6CS-2d Specimen and Load-Displacement for S1 Specimen Response

(1) GFRP-ReinforcedSlab-Column Connection Specimen, G6CS-2d. Figure 21 shows comparison of the unbalanced moment drift ratio response obtained from NLFEA compared with the experimental results of the specimen G6CS-2d.Figure 21
Unbalanced moment drift ratio graph for G6CS-2d specimen.The NLFEA’s unbalanced moment drift ratio response of the specimen GFRP-reinforcedslab-column connection (G6CS-2d) is a good agreement with the experimental result. The maximum unbalanced moment obtained from the NLFEA of this specimen is 1.32% lower than the maximum unbalanced moment reported from the experimental study (see Table5). The higher stiffness observed in NLFEA results as compared to the experimental results might be due to the formation of microcracks in the experimental test, thus reducing its stiffness, whereas in finite element models do not fully capture the development of these microcracks [27]. Also, the perfect bond assumption between concrete and reinforcement in developed finite element models might account for the aforementioned minor differences between NLFEA and experimental results.Table 5
Maximum unbalanced moment and maximum load comparisons of NLFEA prediction with the test results of the two specimens.
SpecimenMaximum lateral load (kN)Maximum unbalanced moment (KN.m)Specimen 1 ID nameNLFEATestError (%)NLFEATestError (%)G6CS–2d148.68150.9−1.47195.985198.6−1.32SpecimenMaximum axial load (KN)PredictionSpecimen 2 ID nameNLFEATestError (%)S1185.211793.47(2) Reinforced Concrete Flat Slab Specimen, S1. As can be seen in Figure 22, the load-displacement curves of NLFEA and experimental results showed good agreement. The maximum load obtained from NLFEA analysis was 3.47% higher than the maximum load reported from the experimental study (see Table 5). Table 5 shows accuracy of NLFEA results for the two specimens as compared with the experimental test results. It describes the overall model accuracy of the NLFEA. The error (%) was evaluated based on the relation given in [28] and as shown in the following:(2)error%=NLFEA−testresulttestresult∗100.Figure 22
Load-displacement curve for specimen S1.In all cases, the FEA results of the connection punching shear cracking, unbalanced moment, and maximum load fall to an error of less than 5% implying that the finite element response of the specimens is in good agreement with experimental test results. This indicates that employed material properties and constitutive models were capable of capturing the response of GFRP-reinforcedslab-column connection with GFRP shear reinforcement.


### 3.1.2. Failure Patternsald

(1) GFRP-ReinforcedSlab-Column Connection Specimen, G6CS-2d. Figure 23 shows side by side comparison of crack patterns of NLFEA and experimental test results at failure load for specimens G6CS-2d.Figure 23
Comparison of concrete damage of specimen G6CS-2d at failure load. (a) Experimental half-scale [8]. (b) FEA half-scale plan view. (c) FEA half-scale 3D view.
(a)(b)(c)Figure23 shows that the numerical model shows good agreement between the punching shear cracking pattern obtained from NLFEA and the punching shear crack propagation pattern reported in the experimental study. In both results, punching cracking patterns concentrated on GFRP-reinforcedslab-column connection.(2) Reinforced Concrete Flat Slab Specimen, S1. Figure 24 presents FEA temperature distributions of flat slab specimen, S1 after 3600sec fire exposure, whereas Figure 25 shows the comparison of crack patterns in specimens S1 between NLFEA and experimental test results at the failure load stage.Figure 24
FEA temperature distributions after 3600 sec fire exposure at the bottom of specimen S1 slab.Figure 25
Comparison of concrete damage of specimen S1 due to 3600 sec fire exposure and maximum load. (a) Experimental half-scale [11]. (b) FEA half-scale plan view. (c) FEA half-scale 3D view.
(a)(b)(c)Overall failure patterns as predicted by NLFEA showed good agreement with experimental test results. Therefore, developed FE models can be used as an effective and reliable tool to study effect of various influential parameters on post-earthquake fire punching shear behavior of GFRP-reinforcedslab-column connections.Aforementioned validated FE model was used as a controlling specimen of GFRP-reinforcedslab-column connection with GFRP shear reinforcement provided at 2d from the face of the column under an earthquake and axial load at ambient temperature. Then, in subsequent parametric studies, the validated FE model was subjected to post-earthquake fire at the bottom surface of the slab besides to lateral load and 0%, 10%, 20%, and 50% axial loading levels. Nevertheless, except for the aforementioned applied loads, the control specimen’s detailing had been kept identical to the experimental test in [3]. FEA results such as unbalanced moment drift ratio and drift ratio-fire duration response for an all-varied axial load level loading are discussed below.Figures26–29 show the effect of varied axial load levels on the unbalanced moment drift ratio and drift ratio-fire duration response. FEA results showed that changes in axial loading levels affected slab-column connection fire resistance performance. As the axial load ratio increased from 0% to 10% to 20% and 50%, slab-column connection fire resistance reduced to 49.87 min, 25.48 min, 5.48 min, and 4.65 min, respectively. For subsequent parametric studies, a FE model with 0% axial load level, 3.07% drift ratio, and 40 min post-earthquake fire exposure duration was used as a control specimen. Next, Figures 30–33 present nodal temperature distribution, unbalanced moment drift ratio, homogenized concrete damage, and rebar strain for a 0% axial load level control specimen.Figure 26
(a) Unbalanced moment drift ratio response and (b) drift ratio-fire exposed duration response of 0% axial load level.
(a)(b)Figure 27
(a) Unbalanced moment drift ratio response and (b) drift ratio-fire exposed duration response of 10% axial load level.
(a)(b)Figure 28
(a) Unbalanced moment drift ratio response and (b) drift ratio-fire exposed duration response of 20% axial load level.
(a)(b)Figure 29
(a) Unbalanced moment drift ratio response and (b) drift ratio-fire exposed duration response of 50% axial load level.
(a)(b)Figure 30
Nodal temperature distribution of control specimen with 2400 sec fire exposure at the bottom surface of slab. (a) 3D view of nodal temperature distribution of the control specimen. (b) Centerline section view of nodal temperature distribution of the control specimen.
(a)(b)Figure 31
The control specimen’s time versus temperature behavior during a 2400 sec fire exposure at the bottom surface of a slab at varying slab depths.Figure 32
Control specimen’s unbalanced moment drift ratio response with 2400 sec fire exposure.Figure 33
Total concrete damage to control specimen due to 2400 sec fire exposure at the bottom of the slab. (a) Total concrete damage at maximum load. (b) Bottom surface total concrete damage at maximum load. (c) Total concrete damage at failure load. (d) Bottom surface total concrete damage at failure load.
(a)(b)(c)(d)


## 3.1.1. Unbalanced Moment Drift Ratio for G6CS-2d Specimen and Load-Displacement for S1 Specimen Response

(1) GFRP-ReinforcedSlab-Column Connection Specimen, G6CS-2d. Figure 21 shows comparison of the unbalanced moment drift ratio response obtained from NLFEA compared with the experimental results of the specimen G6CS-2d.Figure 21
Unbalanced moment drift ratio graph for G6CS-2d specimen.The NLFEA’s unbalanced moment drift ratio response of the specimen GFRP-reinforcedslab-column connection (G6CS-2d) is a good agreement with the experimental result. The maximum unbalanced moment obtained from the NLFEA of this specimen is 1.32% lower than the maximum unbalanced moment reported from the experimental study (see Table5). The higher stiffness observed in NLFEA results as compared to the experimental results might be due to the formation of microcracks in the experimental test, thus reducing its stiffness, whereas in finite element models do not fully capture the development of these microcracks [27]. Also, the perfect bond assumption between concrete and reinforcement in developed finite element models might account for the aforementioned minor differences between NLFEA and experimental results.Table 5
Maximum unbalanced moment and maximum load comparisons of NLFEA prediction with the test results of the two specimens.
SpecimenMaximum lateral load (kN)Maximum unbalanced moment (KN.m)Specimen 1 ID nameNLFEATestError (%)NLFEATestError (%)G6CS–2d148.68150.9−1.47195.985198.6−1.32SpecimenMaximum axial load (KN)PredictionSpecimen 2 ID nameNLFEATestError (%)S1185.211793.47(2) Reinforced Concrete Flat Slab Specimen, S1. As can be seen in Figure 22, the load-displacement curves of NLFEA and experimental results showed good agreement. The maximum load obtained from NLFEA analysis was 3.47% higher than the maximum load reported from the experimental study (see Table 5). Table 5 shows accuracy of NLFEA results for the two specimens as compared with the experimental test results. It describes the overall model accuracy of the NLFEA. The error (%) was evaluated based on the relation given in [28] and as shown in the following:(2)error%=NLFEA−testresulttestresult∗100.Figure 22
Load-displacement curve for specimen S1.In all cases, the FEA results of the connection punching shear cracking, unbalanced moment, and maximum load fall to an error of less than 5% implying that the finite element response of the specimens is in good agreement with experimental test results. This indicates that employed material properties and constitutive models were capable of capturing the response of GFRP-reinforcedslab-column connection with GFRP shear reinforcement.


## 3.1.2. Failure Patternsald

(1) GFRP-ReinforcedSlab-Column Connection Specimen, G6CS-2d. Figure 23 shows side by side comparison of crack patterns of NLFEA and experimental test results at failure load for specimens G6CS-2d.Figure 23
Comparison of concrete damage of specimen G6CS-2d at failure load. (a) Experimental half-scale [8]. (b) FEA half-scale plan view. (c) FEA half-scale 3D view.
(a)(b)(c)Figure23 shows that the numerical model shows good agreement between the punching shear cracking pattern obtained from NLFEA and the punching shear crack propagation pattern reported in the experimental study. In both results, punching cracking patterns concentrated on GFRP-reinforcedslab-column connection.(2) Reinforced Concrete Flat Slab Specimen, S1. Figure 24 presents FEA temperature distributions of flat slab specimen, S1 after 3600sec fire exposure, whereas Figure 25 shows the comparison of crack patterns in specimens S1 between NLFEA and experimental test results at the failure load stage.Figure 24
FEA temperature distributions after 3600 sec fire exposure at the bottom of specimen S1 slab.Figure 25
Comparison of concrete damage of specimen S1 due to 3600 sec fire exposure and maximum load. (a) Experimental half-scale [11]. (b) FEA half-scale plan view. (c) FEA half-scale 3D view.
(a)(b)(c)Overall failure patterns as predicted by NLFEA showed good agreement with experimental test results. Therefore, developed FE models can be used as an effective and reliable tool to study effect of various influential parameters on post-earthquake fire punching shear behavior of GFRP-reinforcedslab-column connections.Aforementioned validated FE model was used as a controlling specimen of GFRP-reinforcedslab-column connection with GFRP shear reinforcement provided at 2d from the face of the column under an earthquake and axial load at ambient temperature. Then, in subsequent parametric studies, the validated FE model was subjected to post-earthquake fire at the bottom surface of the slab besides to lateral load and 0%, 10%, 20%, and 50% axial loading levels. Nevertheless, except for the aforementioned applied loads, the control specimen’s detailing had been kept identical to the experimental test in [3]. FEA results such as unbalanced moment drift ratio and drift ratio-fire duration response for an all-varied axial load level loading are discussed below.Figures26–29 show the effect of varied axial load levels on the unbalanced moment drift ratio and drift ratio-fire duration response. FEA results showed that changes in axial loading levels affected slab-column connection fire resistance performance. As the axial load ratio increased from 0% to 10% to 20% and 50%, slab-column connection fire resistance reduced to 49.87 min, 25.48 min, 5.48 min, and 4.65 min, respectively. For subsequent parametric studies, a FE model with 0% axial load level, 3.07% drift ratio, and 40 min post-earthquake fire exposure duration was used as a control specimen. Next, Figures 30–33 present nodal temperature distribution, unbalanced moment drift ratio, homogenized concrete damage, and rebar strain for a 0% axial load level control specimen.Figure 26
(a) Unbalanced moment drift ratio response and (b) drift ratio-fire exposed duration response of 0% axial load level.
(a)(b)Figure 27
(a) Unbalanced moment drift ratio response and (b) drift ratio-fire exposed duration response of 10% axial load level.
(a)(b)Figure 28
(a) Unbalanced moment drift ratio response and (b) drift ratio-fire exposed duration response of 20% axial load level.
(a)(b)Figure 29
(a) Unbalanced moment drift ratio response and (b) drift ratio-fire exposed duration response of 50% axial load level.
(a)(b)Figure 30
Nodal temperature distribution of control specimen with 2400 sec fire exposure at the bottom surface of slab. (a) 3D view of nodal temperature distribution of the control specimen. (b) Centerline section view of nodal temperature distribution of the control specimen.
(a)(b)Figure 31
The control specimen’s time versus temperature behavior during a 2400 sec fire exposure at the bottom surface of a slab at varying slab depths.Figure 32
Control specimen’s unbalanced moment drift ratio response with 2400 sec fire exposure.Figure 33
Total concrete damage to control specimen due to 2400 sec fire exposure at the bottom of the slab. (a) Total concrete damage at maximum load. (b) Bottom surface total concrete damage at maximum load. (c) Total concrete damage at failure load. (d) Bottom surface total concrete damage at failure load.
(a)(b)(c)(d)


## 3.2. FEA Parametric Studies on GFRP-ReinforcedSlab-Column Connections with GFRP Shear Reinforcement Subjected to Post-Earthquake Fire

This section presents the response of GFRP-reinforcedslab-column connections with GFRP shear reinforcement provided at 2d from the face of the column under post-earthquake fire loading. Effects of influential parameters such as fire exposure duration, concrete grade, slab thickness, fire exposed surface, and column aspect ratio are investigated thoroughly.


### 3.2.1. Effect of Post-Earthquake Fire Exposure Duration

Three different fire exposure durations of 600, 1200, and 1800 seconds were selected and applied to study the impact of fire exposure duration on GFRP-reinforcedslab-column connections under post-earthquake fire loading. Next, the unbalanced moment drift ratio and concrete damage results of these specimens are examined in contrast to the control specimen.FEA results of GFRP-reinforcedslab-column connections under post-earthquake fire exposure for durations of 1800, 1200, and 600 seconds exhibited maximum unbalanced moment of 174.60 KN·m, 179.28 KN·m, and 187.77 KN·m, respectively (Figure34). A decrease in post-earthquake fire exposure duration from 2400 to 600 seconds resulted in peak of unbalanced moment drift ratio in slab-column connections in ranges of 1.89% to 9.58%. This implies higher post-earthquake fire exposure results in increase in temperature distribution of a specimen leading to deterioration of concrete and reinforcement material properties.Figure 34
Effect of post-earthquake fire exposure duration on unbalanced moment drift ratio response.Figure35 presents the nodal temperature distribution for various post-earthquake fire duration and as post-earthquake fire duration increased, so does concrete damages in respective specimens.Figure 35
Concrete damage of specimens with varying post-earthquake fire exposure durations. (a) Specimen 200-45-1-ALL Bs-1800. (b) Bottom surface. (c) Specimen 200-45-1-ALL Bs-1200. (d) Bottom surface. (e) Specimen 200-45-1-ALL Bs-600. (f) Bottom surface.
(a)(b)(c)(d)(e)(f)


### 3.2.2. Effect of Concrete Grade

Analytical formulas in ACI and Eurocode codes of practice use compressive strength of concrete as a key parameter to evaluate punching shear stress of concrete slab. The control specimen has C-45 MPa concrete grade, and the current parametric study on grade of concrete three different concrete grades was considered, namely, C-25 MPa, C-30 MPa, and C-35 MPa.Figure36 shows that the increasing concrete grade leads to an increase in punching shear capacity. Maximum unbalanced moment of 125.48 KN·m, 138.60 KN·m, and 150.48 KN·m was recorded for GFRP-reinforcedslab-column connections with concrete grades of C-25, C-30, and C-35, respectively, and as compared to control, the losses were −26.77%,−19.11%, and −12.18%. Raising concrete grade has shown better punching shear carrying capacity of GFRP-reinforcedslab-column connections subjected to post-earthquake fire.Figure 36
Effect of concrete grade on unbalanced moment drift ratio.Figure37 shows FEA concrete damage results of GFRP-reinforcedslab-column connections subjected to post-earthquake fire for concrete grades C-25, C-30, and C-35. The results imply that concrete grade has minor effect on lessening concrete damage.Figure 37
Concrete damage of specimens with varying concrete grade. (a) Specimen 200-25-1-ALL Bs-2400. (b) Bottom surface. (c) Specimen 200-30-1-ALL Bs-2400. (d) Bottom surface. (e) Specimen 200-35-1-ALL Bs-2400. (f) Bottom surface.
(a)(b)(c)(d)(e)(f)


### 3.2.3. Effect of Slab Thickness

Three different slab thicknesses of 150 mm, 175 mm, and 250 mm were selected to study effect of slab thickness on behavior of GFRP-reinforcedslab-column connections subjected to post-earthquake fire. FEA results showed thickness of the slab affected structural performance of GFRP-reinforcedslab-column connections subjected to post-earthquake fire.FEA results for slab thicknesses of 150 mm, 175 mm, and 250 mm displayed ultimate moment of 133.24 KN·m, 162.34 KN·m, and 210.50 KN·m (Figure38), and as compared to control, variations were −22.24%, −5.26%, and 22.85%. Increasing slab thickness decreased heat transfer across slab section resulting minor concrete deterioration. Moreover, increasing slab thickness enlarged effective depth of the specimens which in turn raised shear resistance of concrete due to aggregate interlocking.Figure 38
Effect of slab thickens on unbalanced moment drift ratio.Figure39 presents the nodal temperature variations for GFRP-reinforcedslab-column connections with slab thicknesses of 150 mm, 175 mm, and 250 mm. As slab thickness increased, the nodal temperature variations across slab thickness were reduced.Figure 39
Concrete damage of specimens with varying slab thickness. (a) Specimen 150-45-1-ALL Bs-2400. (b) Bottom surface. (c) Specimen 175-45-1-ALL Bs-2400. (d) Bottom surface. (e) Specimen 250-45-1-ALL Bs-2400. (f) Bottom surface.
(a)(b)(c)(d)(e)(f)


### 3.2.4. Effect of Fire Exposed Surface

Three varied surface areas such as all top slab surface, half top slab surface, and half bottom slab surface were selected, and post-earthquake fire loading was applied on aforementioned proposed exposed surfaces of slab to study impact of exposed surface on post-earthquake fire behavior of GFRP-reinforcedslab-column connection.FEA results indicated that as compared to control, maximum unbalanced moment peaked by 7.73%, 14.18%, and 14.29% for specimens with post-earthquake fire exposed surfaces of all top slab surface, half top slab surface, and half bottom slab, respectively. Also, results show that post-earthquake fire exposed to the bottom surface exhibits a higher punching strength structural performance loss than the other two (Figure40).Figure 40
Effect of post-earthquake fire exposed surfaces on unbalanced moment drift ratio.Figure41 presents concrete damage for various post-earthquake fire exposed surfaces. Top surface of slab fire exposure exhibited higher concrete damage than the bottom surface of slab fire exposure. This can be accounted to the lower top reinforcement ratio as compared to the bottom GFRP-reinforcedslab-column connection.Figure 41
Concrete damage of specimens with varying fire exposed surface. (a) Specimen 200-45-1-ALL TS-2400. (b) Bottom surface. (c) Specimen 200-45-1-Half TS-2400. (d) Bottom surface. (e) Specimen 200-45-1-Half BS-2400. (f) Bottom surface.
(a)(b)(c)(d)(e)(f)


### 3.2.5. Effect of Column Rectangularity (Aspect Ratio)

The column aspect ratio, or rectangularity, is calculated by the ratio of lengths of long and short sides of a column. Column rectangularity would have an impact on the punching capacity of flat plates by reducing the shear stress capacity along the critical perimeter. This hypothesis was tested by considering three different column rectangularity indexes (β = 1.16, 1.33, and 1.66) on GFRP-reinforcedslab-column connection under post-earthquake fire loading.FEA results showed that as compared to control (β = 1), GFRP-reinforcedslab-column connection with column aspect ratios of 300 × 350 mm (β = 1.16), 300 × 400 mm (β = 1.33), and 300 × 500 mm (β = 1.66) exhibited ultimate moments increments of 21.41%, 51.53%, and 99.21%, respectively (Figure 42). Increasing column aspect ratio decreased shear stress capacity along the critical perimeter and pushed failure perimeters away from the column.Figure 42
Effect of column aspect ratio on unbalanced moment drift ratio.Figure43 presents concrete damages for GFRP-reinforcedslab-column connection models under post-earthquake fire with various column aspect ratio. Column aspect ratio increment has illustrated a higher effect on decreasing concrete damage relative to gains in unbalanced moment drift ratios. This is attributed to column aspect ratio increments lead failure perimeters away from the column, which indirectly lessens concrete damage. However, at an aspect ratio of 1.66, concrete damage increased as compared to others. This can be accounted to the formation of stress concentration at the corner location of the column.Figure 43
Concrete damage of specimens with varying column aspect ratio. (a) Specimen 200-45-1.166-ALL BS-2400. (b) Bottom surface. (c) Specimen 200-45-1.333-ALL BS-2400. (d) Bottom surface. (e) Specimen 200-45-1.666-ALL BS-2400. (f) Bottom surface.
(a)(b)(c)(d)(e)(f)


## 3.2.1. Effect of Post-Earthquake Fire Exposure Duration

Three different fire exposure durations of 600, 1200, and 1800 seconds were selected and applied to study the impact of fire exposure duration on GFRP-reinforcedslab-column connections under post-earthquake fire loading. Next, the unbalanced moment drift ratio and concrete damage results of these specimens are examined in contrast to the control specimen.FEA results of GFRP-reinforcedslab-column connections under post-earthquake fire exposure for durations of 1800, 1200, and 600 seconds exhibited maximum unbalanced moment of 174.60 KN·m, 179.28 KN·m, and 187.77 KN·m, respectively (Figure34). A decrease in post-earthquake fire exposure duration from 2400 to 600 seconds resulted in peak of unbalanced moment drift ratio in slab-column connections in ranges of 1.89% to 9.58%. This implies higher post-earthquake fire exposure results in increase in temperature distribution of a specimen leading to deterioration of concrete and reinforcement material properties.Figure 34
Effect of post-earthquake fire exposure duration on unbalanced moment drift ratio response.Figure35 presents the nodal temperature distribution for various post-earthquake fire duration and as post-earthquake fire duration increased, so does concrete damages in respective specimens.Figure 35
Concrete damage of specimens with varying post-earthquake fire exposure durations. (a) Specimen 200-45-1-ALL Bs-1800. (b) Bottom surface. (c) Specimen 200-45-1-ALL Bs-1200. (d) Bottom surface. (e) Specimen 200-45-1-ALL Bs-600. (f) Bottom surface.
(a)(b)(c)(d)(e)(f)


## 3.2.2. Effect of Concrete Grade

Analytical formulas in ACI and Eurocode codes of practice use compressive strength of concrete as a key parameter to evaluate punching shear stress of concrete slab. The control specimen has C-45 MPa concrete grade, and the current parametric study on grade of concrete three different concrete grades was considered, namely, C-25 MPa, C-30 MPa, and C-35 MPa.Figure36 shows that the increasing concrete grade leads to an increase in punching shear capacity. Maximum unbalanced moment of 125.48 KN·m, 138.60 KN·m, and 150.48 KN·m was recorded for GFRP-reinforcedslab-column connections with concrete grades of C-25, C-30, and C-35, respectively, and as compared to control, the losses were −26.77%,−19.11%, and −12.18%. Raising concrete grade has shown better punching shear carrying capacity of GFRP-reinforcedslab-column connections subjected to post-earthquake fire.Figure 36
Effect of concrete grade on unbalanced moment drift ratio.Figure37 shows FEA concrete damage results of GFRP-reinforcedslab-column connections subjected to post-earthquake fire for concrete grades C-25, C-30, and C-35. The results imply that concrete grade has minor effect on lessening concrete damage.Figure 37
Concrete damage of specimens with varying concrete grade. (a) Specimen 200-25-1-ALL Bs-2400. (b) Bottom surface. (c) Specimen 200-30-1-ALL Bs-2400. (d) Bottom surface. (e) Specimen 200-35-1-ALL Bs-2400. (f) Bottom surface.
(a)(b)(c)(d)(e)(f)


## 3.2.3. Effect of Slab Thickness

Three different slab thicknesses of 150 mm, 175 mm, and 250 mm were selected to study effect of slab thickness on behavior of GFRP-reinforcedslab-column connections subjected to post-earthquake fire. FEA results showed thickness of the slab affected structural performance of GFRP-reinforcedslab-column connections subjected to post-earthquake fire.FEA results for slab thicknesses of 150 mm, 175 mm, and 250 mm displayed ultimate moment of 133.24 KN·m, 162.34 KN·m, and 210.50 KN·m (Figure38), and as compared to control, variations were −22.24%, −5.26%, and 22.85%. Increasing slab thickness decreased heat transfer across slab section resulting minor concrete deterioration. Moreover, increasing slab thickness enlarged effective depth of the specimens which in turn raised shear resistance of concrete due to aggregate interlocking.Figure 38
Effect of slab thickens on unbalanced moment drift ratio.Figure39 presents the nodal temperature variations for GFRP-reinforcedslab-column connections with slab thicknesses of 150 mm, 175 mm, and 250 mm. As slab thickness increased, the nodal temperature variations across slab thickness were reduced.Figure 39
Concrete damage of specimens with varying slab thickness. (a) Specimen 150-45-1-ALL Bs-2400. (b) Bottom surface. (c) Specimen 175-45-1-ALL Bs-2400. (d) Bottom surface. (e) Specimen 250-45-1-ALL Bs-2400. (f) Bottom surface.
(a)(b)(c)(d)(e)(f)


## 3.2.4. Effect of Fire Exposed Surface

Three varied surface areas such as all top slab surface, half top slab surface, and half bottom slab surface were selected, and post-earthquake fire loading was applied on aforementioned proposed exposed surfaces of slab to study impact of exposed surface on post-earthquake fire behavior of GFRP-reinforcedslab-column connection.FEA results indicated that as compared to control, maximum unbalanced moment peaked by 7.73%, 14.18%, and 14.29% for specimens with post-earthquake fire exposed surfaces of all top slab surface, half top slab surface, and half bottom slab, respectively. Also, results show that post-earthquake fire exposed to the bottom surface exhibits a higher punching strength structural performance loss than the other two (Figure40).Figure 40
Effect of post-earthquake fire exposed surfaces on unbalanced moment drift ratio.Figure41 presents concrete damage for various post-earthquake fire exposed surfaces. Top surface of slab fire exposure exhibited higher concrete damage than the bottom surface of slab fire exposure. This can be accounted to the lower top reinforcement ratio as compared to the bottom GFRP-reinforcedslab-column connection.Figure 41
Concrete damage of specimens with varying fire exposed surface. (a) Specimen 200-45-1-ALL TS-2400. (b) Bottom surface. (c) Specimen 200-45-1-Half TS-2400. (d) Bottom surface. (e) Specimen 200-45-1-Half BS-2400. (f) Bottom surface.
(a)(b)(c)(d)(e)(f)


## 3.2.5. Effect of Column Rectangularity (Aspect Ratio)

The column aspect ratio, or rectangularity, is calculated by the ratio of lengths of long and short sides of a column. Column rectangularity would have an impact on the punching capacity of flat plates by reducing the shear stress capacity along the critical perimeter. This hypothesis was tested by considering three different column rectangularity indexes (β = 1.16, 1.33, and 1.66) on GFRP-reinforcedslab-column connection under post-earthquake fire loading.FEA results showed that as compared to control (β = 1), GFRP-reinforcedslab-column connection with column aspect ratios of 300 × 350 mm (β = 1.16), 300 × 400 mm (β = 1.33), and 300 × 500 mm (β = 1.66) exhibited ultimate moments increments of 21.41%, 51.53%, and 99.21%, respectively (Figure 42). Increasing column aspect ratio decreased shear stress capacity along the critical perimeter and pushed failure perimeters away from the column.Figure 42
Effect of column aspect ratio on unbalanced moment drift ratio.Figure43 presents concrete damages for GFRP-reinforcedslab-column connection models under post-earthquake fire with various column aspect ratio. Column aspect ratio increment has illustrated a higher effect on decreasing concrete damage relative to gains in unbalanced moment drift ratios. This is attributed to column aspect ratio increments lead failure perimeters away from the column, which indirectly lessens concrete damage. However, at an aspect ratio of 1.66, concrete damage increased as compared to others. This can be accounted to the formation of stress concentration at the corner location of the column.Figure 43
Concrete damage of specimens with varying column aspect ratio. (a) Specimen 200-45-1.166-ALL BS-2400. (b) Bottom surface. (c) Specimen 200-45-1.333-ALL BS-2400. (d) Bottom surface. (e) Specimen 200-45-1.666-ALL BS-2400. (f) Bottom surface.
(a)(b)(c)(d)(e)(f)


## 4. Conclusions

In this study, behavior of interior GFRP-reinforcedslab-column connections with GFRP shear reinforcement provided at 2 d from the face of the column under post-earthquake fire was investigated. Influential parameters such as effects of post-earthquake fire exposure duration, concrete grade, slab thickness, post-earthquake fire exposure surfaces, and column aspect ratio (regularity index) were studied to learn response of on GFRP-reinforcedslab-column connections when subjected to post-earthquake fire.(i)
Post-earthquake fire exposure duration affects the punching shear carrying capacity of GFRP-reinforcedslab-column connections. As compared to the control, post-earthquake fire exposure duration decrement from 1800 seconds to 600 seconds increased the punching shear carrying capacity by 1.89% to 9.58%.(ii)
Concrete grade influences post-earthquake fire punching shear carrying capacity of GFRP-reinforcedslab-column connections. As compared to the control (C45 MPa), decreasing concrete grade from C35 Mpa to C25 Mpa decreased punching shear carrying capacity by −12.18% to −26.77%.(iii)
Slab thickness impacts post-earthquake fire punching shear carrying capacity of GFRP-reinforcedslab-column connections. As compared to control (slab thickness 200 mm), GFRP-reinforcedslab-column connections with slab thickens of 150 mm to 250 mm, improved the punching shear carrying capacity by −22.24% to 22.85%.(iv)
Location of post-earthquake fire exposed surfaces affects response of GFRP-reinforcedslab-column connections. As compared to the control (all slab bottom face post-earthquake fire exposure), post-earthquake fire exposure of all top slab surface, half top slab surface, and half bottom slab surface exhibited 7.74%, 14.18, and 14.29% gain in punching shear carrying of GFRP-reinforcedslab-column connection, respectively.(v)
Among considered parameters, column rectangularity has a higher impact on post-earthquake fire punching shear carrying capacity of GFRP-reinforcedslab-column connections. As compared to the control (β = 1), increasing column rectangularity from 1.16 to 1.66 resulted in 21.41% to 99.21% gain in punching shear carrying of GFRP-reinforcedslab-column connection.



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*Source: 7596032-2023-02-23.xml*