bluuebunny/crossref_metadata_2025 huggingface dataset:
Effect of parameters on butyl butyrate synthesis using novel Aspergillus niger lipase as biocatalyst
Authors: Travalia Beatriz Medeiros , Galvão Mercia , Lima Alvaro Silva , Soares Cleide Mara Faria , Narain Narendra , Santana Luciana Cristina Lins de Aquino
Published: July 2018

A novel “green” Aspergillus niger lipase, obtained from the fermentation of pumpkin seeds, was used in a free form and encapsulated in sol-gel matri x in butyl butyrate (pineapple flavor) synthesis. Esterification reactions were performed with varying substrate molar ratio (butanol: butyric acid) ranging between 1:1 and 5:1; temperature between 30 and 60°C and biocatalyst mass between 0 and 1g, respectively, according to experimental design 23 with 6 axial and 3 central points. Maximum butyl butyrate production was obtained when substrate molar ratio (butanol:butyric acid) 3:1, temperature at 60°C and 0.5 g free or encapsulated lipase as biocatalyst, were used. Temperature was the most significant parameter for production with the two biocatalysts, indicating that higher rates mean greater compound synthesis. Response surface plots showed that higher butyl butyrate production may be obtained with higher temperature and molar ratio rates (butanol:butyric acid) and with lower rates of biocatalyst mass in reactions catalyzed by free or encapsulated lipase. Aspergillus niger lipase obtained from agro-industrial waste could be employed as biocatalyst in esterification reactions in the production of natural aroma as butyl butyrate.
Hypercalcemia associated with squamous cell carcinoma of renal pelvis
Authors: Musri Fatma Yalcin , Mutlu Hasan , Eryilmaz Melek Karakurt , Salim Derya Kivrak , Tazegul Gokhan , Coşkun Hasan Şenol
Published: July 2018

Renal pelvis squamous cell carcinoma (RSCC) is a rare tumor. It starts with nonspecific symptoms and it is usually at an advanced stage with a poor prognosis at the time of diagnosis. SCC-associated hypercalcemia is a well-known paraneoplastic syndrome; however RSCC-associated hypercalcemia is a rare condition. Our patient is a 57-year-old-male patient with no bone metastases. Based on the literature screening on PubMed Database for paraneoplastic malignant hypercalcemia-associated RSCC, we found a few cases.
An audit of gastrointestinal stromal tumors from a tertiary medical college hospital in Eastern India
Authors: Dutta Samrat , Ghosh Bidisha , Pal Rupsha , Pandey Prashant , Mukhopadhyay Madhumita , Saklani Amit , Chatterjee Kaustav
Published: July 2018

Introduction: Gastrointestinal stromal tumors (GIST) are the most common mesenchymal tumors of GI tract. They are recently recognized as a distinct pathological entity although previously they were grouped with sarcomas of smooth muscle origin, i.e., leiomyomas, leiomyoblastomas, or leiomyosarcomas. However, apart from GI tract, GIST can occur in any smooth muscle-like in the urinary bladder. Proper diagnosis by immunohistochemistry stain CD133 and risk stratification by morphological parameters has been the cornerstone of treatment.

Materials and Methods: This study was conducted as a retrospective analysis to audit the number of cases presenting as GIST in the tertiary medical colleges of eastern India and find out the patterns of care with the available modalities of therapy.

Results: Out of total 15 cases, the median age of presentation was 45 years; the Male: Female (M: F) ratio was 2:3 and persisting dragging prolonged chronic abdominal pain was present in the majority. Intestinal complications were few (20%). All were treated with imatinib mesylate 400 mg once daily. However, two patients progressed for whom the dose of imatinib was escalated and one patient was metastatic at onset who was later switched over to sorafenib even after disease progression with dose escalation with imatinib. The median follow-up was 17.5 months and the median time to response to imatinib was 3.2 months. The 2-year actuarial overall survival was 79.12%, and progression-free survival was 86.67%.

Conclusions: The future directions are to determine appropriate duration of imatinib therapy in adjuvant/neoadjuvant and therapeutic setting.
Pleuropericardial mesotheliomas: A report of two unusual cases
Authors: Ramanjaneyulu Harsha Vardhana Kuruba , Kapoor Anu , Biswal Chinmayee , Mutnuru Phani Chakravrty
Published: July 2018

Mesothelioma is an aggressive malignant tumor of the mesothelium. The majority of mesotheliomas arise from the pleura. However, less commonly mesothelioma can arise in other locations such as peritoneal, pericardium, or tunica vaginalis testis. We report two rare cases here, one with pericardial mesothelioma and another with malignant pleural mesothelioma with synchronous colonic carcinoma. The clinical, radiological, and pathology findings in these cases are discussed along with a brief review of pertinent literature.
The impact of economic policy and structural change on gender employment inequality in Latin America, 1990–2010
Authors: Braunstein Elissa , Seguino Stephanie
Published: July 2018

Latin America experienced a decline in household income inequality in the 2000s, in sharp contrast to growing inequality in other regions of the world. This has been attributed to macroeconomic policy, social spending, and increased returns to education. This paper explores this issue from a gender perspective by econometrically evaluating how changes in economic structure and policy have impacted gendered employment and unemployment rates, as well as gender inequality in these variables, using country-level panel data for a set of 18 Latin American countries between 1990 and 2010. Three variables stand out as having consistent gender-equalizing effects in the labor market: social spending, minimum wages, and public investment. Less important or consistent were the effects of external factors (such as terms of trade), economic structure, and GDP growth.
Growth dilemmas in open middle-income economies: a reflection on Mexico's recent experience*
Authors: López G. Julio
Published: July 2018

This paper proposes an explanation of Mexico's economic evolution during the period in which its neoliberal strategy has been consolidated and consistently implemented. The focus is on global issues. The paper provides an interpretation of macroeconomic developments and the factors behind Mexico's slow growth, with an emphasis on economic policies and their consequences. A particularly important factor is the phenomenal growth of the import coefficient. On the basis of previous findings, the paper also presents some prospective scenarios for Mexico. The main purpose of the exercises is to show the difficulties faced by Mexico, which is very open to international trade, in combining fast growth with external balance.
Push-Out Tests for a Novel Prefabricated Steel-Concrete Composite Shallow Flooring System
Authors: Ahmed Inas Mahmood , Tsavdaridis Konstantinos Daniel , Neysari Farzad , Forth John
Published: July 2018

This paper introduces a novel prefabricated and shallow steel-concrete composite flooring system which is consisted of two main structural components: two C-channel steel beams and a partially encased concrete floor. The concrete floor, which is in the form of T ribbed slab sections, was constructed using two types of concrete (reinforced normal concrete and reinforced lightweight aggregate concrete). The steel edge beams partially encase the floor slab and provide clear and straight finish edges. The floor slab spans to a maximum of 2.0m inclusive of the width of the steel edges with a finished depth of only 230mm. The unique features of the proposed system are reducing the weight and the number of erection lifts (during installation) by using lighter elements (lightweight concrete and shallow steel beams) while the wider possible units have been proposed to fit on transportation tracks; further reducing the extent of site works by pre-off site fabrication, examining the material cost against the fabrication and site erection costs. For the composite slab in bending, the longitudinal shear force is transferred by a unique shear mechanism which results from the special shear connectors. This paper includes the work of a total 2 full-scale push-out tests aimed at investigating the longitudinal shear behaviour of these novel flooring systems and the effects of additional shear connectors. An analytical work is also carried out to investigate the failure mechanism of the system.
Simplified numerical modelling of rectangular concrete-filled steel columns, beams and beam-columns
Authors: Tao Zhong , Katwal Utsab , Hassan Kamrul , Wang Wen-Da
Published: July 2018

Because of its computational efficiency, simplified numerical modelling is the preferred method to simulate structural frames for routine design. As for concrete-filled steel tubular (CFST) columns, fibre beam element (FBE) modelling is often used in the simplified simulation. However, the accuracy of FBE modelling is greatly affected by the accuracy of the input material models, which should directly account for the interaction between the steel tube and core concrete. In this paper, simple yet accurate material models of steel and concrete are proposed for rectangular CFST columns by utilising a large amount of numerical data generated from detailed three-dimensional finite element modelling of stub columns. The material models are then incorporated into the simplified FBE simulation of rectangular CFST columns, beams and beam-columns. The accuracy of the simplified FBE simulation is verified by a wide range of experimental results on rectangular CFST stub columns, slender columns, beams and beam-columns.
Sustainable steel and composite constructions for multifunctional commercial buildings
Authors: Stroetmann Richard Maria , Hüttig Lukas
Published: July 2018

Rising cost pressures and the prospect of quick returns have led to an increase in mono functional buildings since the 1970s. These prevent the adaptation to changing user requirements with little monetary outlay. Lack of marketability, increasing vacancy and early demolition are often the consequences. Main objective of the AIF/FOSTA research project P1118 is to develop planning recommendations for multifunctional usable buildings. Adaptability to changing needs will increase marketability and value stability as well as extend the lifetime of the buildings. This not only increases the economy but also the resource efficiency. First of all, the paper explains the ecological and economic requirements for modern buildings, which are based on current certification systems. In this context, the expected lifetime of primary and secondary building components are also dealt with. Subsequently, relevant types of use as well as requirements for essential building parameters are presented. In a comparison, the ecological expenses and costs are assessed for four selected composite structures. For the multifunctional building structures an extension of lifetime is considered and the environmental and monetary impacts are assessed. Furthermore, the influence of the structure on the building foundations is analysed. The investigations present the effects of the building masses on the foundations for two different soil conditions. Finally, the investigations show that variable usable buildings with a longer lifetime lead to a better sustainability.
Analytical behaviour of concrete-encased CFST box stub columns under axial compression
Authors: Chen Jin-Yang , Han Lin-Hai , Wang Fa-Cheng , Mu Ting-Min
Published: July 2018

Concrete-encased CFST (concrete-filled steel tube) members have been widely used in high-rise buildings and bridge structures. In this paper, the axial performance of a typical concrete-encased CFST box member with inner CFST and outer reinforced concrete (RC) is investigated. A finite element analysis (FEA) model is established to analyze the compressive behavior of the composite member. The material nonlinearity and the interaction between concrete and steel tube are considered. A good agreement is achieved between the measured and predicted results in terms of the failure mode and the load-deformation relation. The verified FEA model is then used to conduct the full range analysis on the load versus deformation relations. The loading distributions of different components inclouding concrete, steel tube and longitudinal bar during four stages are discussed. Typical failure modes, internal force distribution, stress development and the contact stress between concrete and steel tube are also presented. The parametric study on the compressive behavior is conducted to investigate the effects of various parameters, e.g. the strength of concrete and steel, longitudinal bar ratio and stirrup space on the sectional capacity and the ductility of the concrete-encased CSFT box member.
Compressive behaviour of steel tubes filled with strain hardening cementitious composites
Authors: Tao Zhong , Shuaibu Richard , Pan Zhu , Hassan Md Kamrul , Zhou Jian
Published: July 2018

This paper presents the compressive behaviour of steel tubes filled with strain hardening cementitious composites (SHCC) through experimental and numerical investigations. The main parameters considered in the experimental study include type (SHCC and normal concrete) and strength (normal and high strength) of the in-fill material, steel tube thickness (2 and 4 mm) and cross-section type (circular and square). To develop the SHCC material, 2% of polyvinyl alcohol fibres by volume were used. The test results indicate that the performance of SHCC-filled steel tubes is generally similar to that of the counterparts filled with normal concrete. A finite element (FE) model was then developed to predict the load–deformation curves of the test specimens. In general, a reasonably good match is obtained between the predicted and measured curves.
Resistance of a steel-concrete hybrid thermal break system to low cycle fatigue under thermal actions
Authors: Le Gac Benoit , Keo Pisey , Somja Hugues , Palas Franck
Published: July 2018

External insulation is the most widely used technique in Northern and Continental Europe.  This technique generates thermal bridges where the building facade has some projecting element like balconies.  The thermal requirements of actual standards lead to restore the continuity of the insulation at the interfaces by using thermal break systems (TBS).  They are usually made of a box containing the insulation material, and a minimalist structural system able to transmit the shear force and the bending moment from the balcony to the wall.  In most cases, structural elements are made of stainless steel, as it is less heat-conducting than normal steel.  The paper focuses on a specific TBS, that uses shear keys and steel profiles to ensure the transfer of forces. TBS are also submitted to important horizontal cyclic shear deformations, provoked by the variations of the dimensions of the balconies due to climatic effects.  The objective of the study presented in the paper is to show that significant yielding under these cyclic actions can be accepted during service life.  First experimental cyclic loading tests have been performed in order to characterize the behaviour of the TBS, as well as its fatigue strength.  Then the loading has been defined on the basis of the database of the ECA&D, the European Climate Assessment and Dataset.  Finally, the fatigue resistance of the system has been verified.  It is shown that the developed TBS can resist to fatigue loading for large lengths of balconies, while exhibiting significant yielding during service life.
Behaviour and Design of Composite Steel and Precast Concrete Transom for Railway Bridges Application
Authors: Mirza Olivia , Talos Andrew , Hennessy Matthew , Kirkland Brendan
Published: July 2018

Currently most railway bridges in Australia require the replacement of the timber transoms that reside in the railway system. Composite steel and precast reinforced concrete transoms have been proposed as the replacement for the current timber counterparts. This paper outlines the structural benefits of composite steel-concrete transoms for ballastless tracks when retrofitted to existing railway steel bridges. However, in existing studies, it is found that there is little investigation into the effect of derailment loading on reinforced concrete transoms. Therefore, this paper provides an investigation of derailment impact loading on precast reinforced concrete transoms. The paper herein investigates the derailment impact loading of a train through experimental testing and numerical analysis of conventional reinforced concrete transoms. The paper also evaluates the potential use of 3 different shear connectors; welded shear studs, Lindapter bolts and Ajax bolts. The results of the experimental tests and finite element models are used to determine whether each transom is a viable option for the replacement of the current timber transoms on the existing bridges in Australia and whether they provide a stronger and longer lasting solution to the current transom problem.
Finite element analysis of mechanical behavior of concrete-filled square steel tube short columns with inner I-shaped CFRP profiles subjected to bi-axial eccentric load
Authors: Li Guochang , Zhan Zhichang , Yang Zhijian , Yang Yu
Published: July 2018

The concrete-filed square steel tube with inner I-shaped CFRP profiles short columns under bi-axial eccentric load were investigated by the finite element analysis software ABAQUS. The working mechanism of the composite columns which is under bi-axial eccentric load are investigated by using the stress distribution diagram of steel tube concrete and the I-shaped CFRP profiles. In this paper, the main parameters; eccentric ratio, steel ratio, steel yield strength, concrete compressive strength and CFRP distribution rate of the specimens were investigated to know the mechanical behavior of them. The interaction between the steel tube and the concrete interface at different characteristic points of the composite columns were analyzed. The results showed that the ultimate bearing capacity of the concrete-filed square steel tube with inner I-shaped CFRP profiles short columns under bi-axial eccentric load decrease with the increase of eccentric ratio, the ultimate bearing capacity of the composite columns increase with the increase of steel ratio, steel yield strength, concrete compressive strength and CFRP distribution rate. The contact pressure between the steel tube and the concrete decreased from the corner zone to the flat zone, and the contact pressure decreased from the mid-height cross section to other sections.
Cooperative work behavior of high strength concrete-filled square high strength tubular stub columns with inner I-shaped CFRP under axial compression
Authors: Li Guochang , Yang Yu , Yang Zhijian , Zhan Zhichang
Published: July 2018

The finite element software ABAQUS was used to analyze 22 high strength concrete-filled square high strength tubular short columns with inner I-shaped CFRP, all analysis results based on the finite element analysis data, six characteristic points were defined in the load-longitudinal strain curve of composite columns. The shared load of core concrete, square steel tube and inner I-shaped CFRP at different height sections of typical specimen corresponding to each characteristic point were analyzed and the cooperative work behavior of inner I-shaped CFRP, square steel tube and core concrete was analyzed. The results show that the existence of the inner I-shaped CFRP can effectively improve the ultimate bearing capacity composite columns, the middle region I-shaped CFRP sharing more longitudinal load than the end region CFRP and the shared load of concrete at the end region section is bigger than that of middle region section, before the CFRP brittle failure. The longitudinal load of square steel tube does not change with the change of the cross-section height.
Behavior of innovative T-shaped multi-partition steel-concrete composite columns under concentric and eccentric compressive loadings
Authors: Zhang Sumei , Chen Jie , Huang Zhenfeng , Zhang Xiongxiong , Guo Lanhui
Published: July 2018

T-shaped multi-partition steel-concrete composite column, composed of several concrete-filled rectangular steel hollow sections, is considered as an innovative composite member with the ability to accommodate neighboring wall thickness with great easiness. This paper intends to study the behavior of this innovative composite member under concentric and eccentric compressive loadings. A finite element (FE) analysis model accounting for the influences of confinement effects, geometric and material nonlinearities is developed using the program ABAQUS. The ultimate strength and load-strain responses predicted from the analysis are validated against the test results in the experiments conducted by the authors. The comparisons indicate that the FE model reasonably estimates the responses of the concentrically and eccentrically loaded T-shaped multi-partition steel-concrete composite columns. The verified model is then utilized to numerically investigate the working mechanism of the columns. The load distribution between the infilled concrete and the steel tubes and the stress distribution of the concrete during the loading process are analyzed. Moreover, parametric studies are performed to investigate the behavior of T-shaped multi-partition steel-concrete composite columns under different loadings. The studied parameters include steel to concrete area ratio, concrete compressive strength, steel yield strength and load eccentricity. Combined with the experimental results, FE analysis and parametric studies, the design recommendations for T-shaped multi-partition steel-concrete composite columns under different loadings are proposed.
Finite element analysis of concrete-encased steel composite columns with off-center steel section
Authors: Liew Jat Yuen Richard , Lai Binglin , Li Shan
Published: July 2018

Concrete encased steel composite columns have been widely used in high-rise buildings and top-down constructions owning to excellent load-carrying capacity and fire resistance. However, double symmetric composite section is rarely achieved due to the off-center eccentricity of steel kingpost, which is a common problem in top-down constructions. EN1994-1-1 (EC4) simplified method does not provide any explicit provisions for this kind of irregular composite columns, and many designers address this issue by reducing it into a symmetrical cross-section for ease of simple calculation. This paper presents a general method based on nonlinear finite element modelling software ABAQUS to analyze the ultimate strength behavior of concrete-encased composite columns with asymmetrically placed steel section. The accuracy of the FE model is verified against existing test results.   Parametric study is performed to further investigate the influence of steel section eccentricity on ultimate strength of stub columns under different loading conditions. A simplified method based on modification of EC4 design approach is developed to construct the moment-axial force interaction diagram. Accuracy of the proposed method is assessed by comparing the analytically predicted results with the numerical results. It is found that the proposed method can be adopted as a useful tool to predict the cross-section resistance of non-symmetrical concrete-encased steel composite columns.
Study on non-buckling steel plate shear walls with corrugated core panel
Authors: Jin Huajian , Li Guoqiang , Sun Feifei
Published: July 2018

In this paper, a non-buckling steel plate shear wall with corrugated core panel was introduced, which keeps itself from premature buckling by fully taking advantage of extra-large flexural stiffness of corrugated core panel and enables to yield before buckling. Most importantly, the optimal corrugation configuration of corrugated core panel was obtained by parametric investigation into detailed dimensions of single wave such as thickness, depth of corrugation, angle of corrugation and so on, which was hereafter validated by numerical simulation. Non-dimensional parameters such as height-to-thickness ratio, width-to-thickness ratio and aspect ratio have also been taken into consideration, all of which turn out to be the most decisive factors of guaranteeing the “non-buckling”. The parametric analysis proves that as long as the former two factors are below the critical values recommended in this paper, unexpected buckling is not going to happen. On the other hand, theoretical approaches to calculate the yielding strength and initial stiffness were derived, as well as a theoretical design method for boundary elements. Meanwhile, a simplified model was concluded. Formulas to determine the cross-section of cross braces and boundary elements were given based on the principle of equivalent yielding strength and initial stiffness. Finally, four specimens were resorted to testify above theory and parametric study. Two specimens with larger height-to-thickness ratio that exceeds the recommended limit exhibit inevitable buckling, while the others with smaller height-to-thickness ratio show ideal energy-absorbing capability and no evident buckling is observed even under an inter-story drift of 2%.
Research progress on material properties of clad steel
Authors: Ban Huiyong , Bai Risheng , Chung Kwok-Fai , Zhu Juncheng , Bai Yin
Published: July 2018

Clad steel possesses benefits of the both component metals in terms of mechanical performance, corrosion resistance, sustainability and lower full lifecycle cost, etc. As a result, it has been more and more widely used in the petroleum, chemical, marine, shipbuilding and metallurgical industries, including stainless-clad steel and titanium clad steel. Such clad steel has also great potential for application in building and bridge structures. For better understanding material properties of such clad steel, a review of research progress available in the literature is conducted herein, as well as recent research undertaken by the authors’ group at Tsinghua University. It can be found that very limited research reported in the literature mainly concerns static material properties of the clad steel, and primary relations between clad ratio and strength are suggested. The authors carried out material tests on both titanium and stainless-clad steel plates, with different clad ratios being incorporated. For the stainless-clad steel tests, both material and butt welded connections are tested, and various elevated temperatures are considered. In addition, tension coupon tests under cyclic loadings are also briefly introduced herein. Primary constitutive relations developed by the authors are reviewed in this paper. All the research findings and proposed formulae may provide an essential basis for future structural analysis, and may promote its application in structural engineering.
Compressive performance of 50 MPa strength concrete-filled square and circular tube (CFT) columns using recycled aggregate
Authors: Choi Sung-Mo , Choi Won Ho , Lee Kangseok , Ryoo Jae-Yong , Kim Sunhee , Park Yong-Pil
Published: July 2018

Recycled aggregate is an environmentally self-sustainable solution that can reduce construction waste and replace natural aggregates. However, there is a disadvantage in concrete such as initial strength drop and long-term strength development. Therefore, the interaction effect of the two materials can be expected by filling the cyclic aggregate concrete in the CFT column. In order to develop a concrete with compressive strength of 50 MPa as a recycled aggregate, we carried out a mixing experiment and fabricated 18 specimens to confirm the compressive behavior of a RCFT (Recycled Concrete Filled Tube) column that can be applied to actual buildings. Variable is the shape and thickness of steel pipe, concrete strength and mixing ratio, and coarse aggregate and fine aggregate are all used as recycled aggregate. The optimum mixing ratio for recycled aggregate concrete to be filled in the CFT filled steel pipe was found through three concrete preliminary mixing experiments. In addition, the compression test of the RCFT column was carried out to observe and analyze the buckling shape of the CFT column. Based on the analysis of the buckling configuration and the experimental data, the load-displacement curves of the specimens were drawn and the compressive behavior was analyzed.
Design for Deconstruction for Sustainable Composite Steel-Concrete Floor Systems
Authors: Hajjar Jerome F. , Wang Lizhong , Webster Mark D.
Published: July 2018

Conventional steel-concrete composite floor systems utilizing steel headed stud anchors and metal decks are cost-effective and widely used solutions for non-residential multi-story buildings, due in part to their enhanced strength and stiffness relative to non-composite systems. Because these systems use steel headed stud anchors welded onto steel flanges and encased in cast-in-place concrete slabs to achieve composite action, it is not possible to readily deconstruct and reuse the steel beams and concrete slabs. As the building industry is moving towards sustainability, there are clear needs for developing sustainable steel-concrete composite floor systems to facilitate material reuse, minimize consumption of raw materials, and reduce end-of-life building waste. This paper presents the behavior and design strategies for a sustainable steel-concrete composite floor system. In this system, deconstructable clamping connectors are utilized to attach precast concrete planks to steel beams to achieve composite action. The load-slip behavior of the clamping connectors was studied in pushout tests, and the test results showed that the clamping connectors possess similar shear strength to 19 mm diameter shear studs and much greater slip capacity. Four full-scale beam tests were performed to investigate the flexural behavior of the deconstructable composite beams under gravity loading and validate the connector behavior attained from the pushout tests. All the beams behaved in a ductile manner. The flexural strengths of the composite beam specimens closely match the strengths predicted for composite beams by the design provisions of the American Institute of Steel Construction (AISC).
The effect of composite floor on the robustness of a steel self-centering MRF under column loss
Authors: Vasdravellis George , Dimopoulos Christoforos , Freddi Fabio , Karavasilis Theodore L
Published: July 2018

This paper presents the numerical assess of the robustness of a seismic-resistant steel building with self-centering moment resisting frames against progressive collapse. The numerical analyses were carried out using a 3D model developed in ABAQUS. The 3D model considers the effect of the composite slab, where composite beams and their shear connectors were modeled with a combination of shell, beam and nonlinear connector elements. All the beam-column and beam-to-beam connections were modeled using nonlinear connector elements with appropriate failure criteria, calibrated against previous experimental results. The self-centering moment resisting frame where a sudden column loss was simulated was modelled using 3D solid elements to accurately capture its local and global nonlinear behavior. Quasi-static nonlinear analyses were carried out to identify all possible failure modes and to investigate the effect of the floor slab on the overall progressive collapse resistance. Nonlinear dynamic analyses were also carried out to predict the true dynamic response and evaluate the acceptance criteria of current building design guidelines.
Influence of joint rigidity on the elastic buckling load of sway and non-sway steel frames
Authors: Ihaddoudène Abd-Nacer-Touati , Saidani Messaoud , Jaspart Jean-Pierre
Published: July 2018

Much work has been conducted in the past on the influence of the rigidity of structural joints on the behavior of steel frames. Buckling of a column is fundamental to the design of load bearing structures mainly when the analysis of such frames takes into account the effect of the connection flexibility. The present work deals with such an effect on the elastic buckling load of plane steel frames. The proposed model consists in the development of comprehensive approach taking into account, the effects of the joint rigidity, the elastic buckling load for both sway and non-sway frames. Only one element is required over the length of the element to model stability, which let to solve practical problem with little computational effort. Some practical formulas for determining critical load for plane steel frames are then presented. The elastic buckling load is found to be strongly affected by semi-rigid joints and reveals that the proposed model is computationally very efficient with the expressions presented being general.
Concrete-encased CFST structures: behaviour and application
Authors: Han Lin-Hai , Ma Dan-Yang , Zhou Kan
Published: July 2018

Concrete-encased CFST (concrete-filled steel tube) is a kind of composite structure comprised of a CFST component and a reinforced concrete (RC) component. The concrete encased CFST possesses superior ductility and higher stiffness. They are gaining popularity in high-rise buildings, large-span structures, bridges, subway stations and workshops. This paper initially reviews the recent research on concrete-encased CFST structures. The major research findings on bond performance, static performance, dynamic performance and fire resistance are presented. This paper also outlines some construction considerations, such as the utilization of materials, the fabrication of the steel tube, and the methods of casting the inner and outer concrete. Finally, some typical practical projects utilizing concrete-encased CFST members are presented and reviewed.
COMPARISON OF DESIGN FOR COMPOSITE COLUMNS IN STEEL AND CONCRETE ACCORDING TO EUROCODE 4 AND CHINESE DESIGN CODES
Authors: Zhang Qingjie , Schäfer Markus
Published: July 2018

This paper compares the design of composite columns in steel and concrete based on EN1994-1-1 and Chinese JGJ138-2016. First, the application ranges of the codes are pointed out. Both codes contain the design of fully encased composite sections and concrete filled rectangular and circular tubes. However, there are different limitations on cross-section sizes, material strength classes, and others. JGJ138 has three separate chapters for the designs related to the three different types of columns. Eurocode 4 gives three different design methods: one general method based on nonlinear calculation, and two simplified methods based on European buckling curves or N-M iteration curves. For the materials, mechanical properties, such as design strength values, are compared based on the same material grade. For axial compression resistance and eccentrically compressive resistance, the two simplified methods from Eurocode 4 are compared with the design method according to JGJ138-2016 through theoretical and parameter studies. The influences of related parameters such as long-term effects, the buckling curves, and N-M iteration curves are also compared. For shear design, JGJ138-2016 considers mainly transverse shear resistances, while Eurocode 4 further considers shear connection and load introduction. The design transverse shear resistance is compared through theory.
Headed studs close to concrete edge under pull-out
Authors: Pascual Ana Maria , Kuhlmann Ulrike , Ruopp Jakob , Stempniewski L.
Published: July 2018

The capacity of the headed studs when they are close to the edge may be limited by the splitting forces in the concrete. In the Eurocode 4 Part 2 Annex C the shear capacity under this particular arrangement of the studs, which is directly dependent on the distance to the edge, is formulated. In addition, the geometrical restrictions to prevent the failure by pull-out of the studs are also given in clause C1 (2). These rules are based on push-out tests for the edge position where tension forces in the lying studs spread over the width of the specimen in this unfavorable way. Nonetheless, the current limits lead to extremely long studs and represent a severe restriction, and on the other hand, it is still an open question whether in real buildings or bridge girders the tension stresses that produce the pull-out appears in the same way as in the push out tests. In this paper the revision of these restrictions is presented together with a research for the alternative use of EN 1992-4 plus RFCS Project INFASO for the verification of the tension loads on the studs.
Numerical evaluation of the plastic hinges developed in headed stud shear connectors in composite beams with profiled steel sheeting
Authors: Vigneri Valentino , Odenbreit Christoph , Braun Matthias
Published: July 2018

For composite beams using novel steel sheeting, the current Eurocode 4 rules sometimes overestimate the load bearing capacity of the shear connector. This is due to the larger rib heights and the smaller rib widths in comparison with the old studies, which have been carried out to calibrate the current design equations. The RFCS Project “DISCCO” investigated this phenomena and the working group under mandate M515, CEN/TC250/SC4/SC4.T3 is enhancing this equation and working on a proposal to be taken over in the new version of Eurocode 4.The proposed new equation covers the failure behaviour of the shear connection more in detail. The test results show, that the failure consists in a combined concrete cone and stud in bending. Due to the geometry of novel steel sheeting, the load bearing capacity of the headed stud shear connector is no more limited by its shear capacity, but by its bending capacity.A 3D non-linear finite element model is developed and validated through the support of the DISCCO push-out tests. A good agreement between numerical and experimental results in terms of force-slip behaviour is achieved. Special attention of this work lies on the numerical evaluation of the number of plastic hinges ny: a stress-based procedure is presented and the results are compared to the equations presented for new Eurocode 4.The numerical simulations show that the upper plastic hinge moves up as the slip increases due to the progressive crushing of the concrete in the rib. From the parametric study, it turns out that ny is linearly proportional to the embedment depth. Compared to pre-punched hole decking, through-deck welding specimen activates less plastic hinges in the studs because of the higher stiffness provided at the base of the stud.
Numerical investigation on slender concrete-filled steel tubular columns subjected to biaxial bending
Authors: Espinós Ana , Albero Vicente , Romero Manuel L. , Mund Maximilian , Kleiboemer Inka , Meyer Patrick , Schaumann Peter
Published: July 2018

The behaviour of concrete-filled steel tubular columns under axial compression or combined compression and uniaxial bending has been deeply investigated in past years by means of experimental testing and numerical simulations. However, the behaviour of these columns under biaxial bending has been scarcely investigated, in fact, a very limited number of experimental tests are available for this loading situation. Additionally, the current provisions in EN1994-1-1 for biaxial bending need to be revised, in order to be aligned with the new methods that are being proposed for the new generation of Eurocodes. This paper presents the outcome of a numerical investigation on the load-bearing capacity of slender concrete-filled steel tubular columns subjected to biaxial bending. The focus is on creating and validating a numerical model for room temperature that can predict the behaviour of this type of columns under biaxial bending, which may be used for evaluating the current design guidelines in EN1994-1-1. The numerical model is validated by comparison against experimental tests from the literature, proving that it predicts the ultimate load of slender columns with good accuracy. Different eccentricities about the minor and major axis and different moment ratios are considered, so that this investigation contains cases for both uniaxial and biaxial bending. With the help of this numerical model, the experimental results are extended to generate more cases, in order to assess the accuracy of the current provisions in EN1994-1-1 for concrete-filled steel tubular columns subjected to biaxial bending.
Factors affecting the response of steel columns to close-in detonations
Authors: Marginean Ioan , Dinu Florea , Dubina Dan , Khalil Ahmed Amir , De Iuliis Emiliano
Published: July 2018

Explosions produced in urban areas by the detonation of explosives are low-probability but high-impact events. When they occur in the immediate vicinity of buildings, the explosions can pose a high risk to the structural integrity (local/global failures) and to the occupants (risk of injury, death). Therefore, the design and the construction of the buildings should contain preventive measures to increase the robustness of the structures. The paper presents the results of recent research carried out on the safety of building structures under extreme actions. Blast tests performed on two identical 3D specimen extracted from a typical moment resisting steel frame structure, allow to calibrate the numerical models of a full scale building structural frame system and evaluate the consequences of close-in detonations on the structural elements. The data of the experimental testing, combined with the numerical modelling, allow to investigate different factors, such as dynamic factors that affect the local failure mechanism and the residual capacity of steel columns under different blast scenarios.
Concrete-filled round-ended steel tubular stub columns under concentric and eccentric loads
Authors: Piquer Vicent Ana , Hernández-Figueirido David , Ibáñez Usach Carmen
Published: July 2018

In the past, many works to study the mechanical behaviour of concrete filled steel tubular (CFST) stub columns have been conducted. Some of the applications of these composite columns oblige to meet higher requirements of ductility and load-bearing capacity. Traditionally, circular and rectangular tubes have been employed but recently new cross-sectional shapes of these composite columns are being designed and investigated with the aim of optimizing their mechanical behaviour. In this line, concrete-filled round-ended steel tubular columns (CFRT) have appeared as an alternative. However, the number of experimental programs to characterize their mechanical response is still scarce. In order to contribute to the test results database, in this paper an experimental study of 9 concrete-filled round-ended steel tubular stub columns is presented. All the specimens were designed with the same cross-sectional round-ended shape and have the same dimensions. In this program, both normal and high-strength concrete were employed as infill. During the tests, the columns were subjected to axial compression loads but under different eccentricities. The influence of eccentricity and concrete strength on the ultimate load bearing capacity of the concrete-filled round-ended steel tubular are discussed. Besides, the combined action of both components in this type of concrete-filled tubes as well as the effect of the concrete infill are studied.
Numerical analysis of concrete-filled spiral welded stainless steel tubes subjected to compression
Authors: Li Dongxu , Uy Brian , Aslani Farhad , Hou Chao
Published: July 2018

Spiral welded stainless tubes are produced by helical welding of a continuous strip of stainless steel. Recently, concrete-filled spiral welded stainless steel tubes have found increasing application in the construction industry due to their ease of fabrication and aesthetic appeal. However, an in-depth understanding of the behaviour of this type of structure is still needed due to the lack of proper design guidance and insufficient experimental verification. In this paper, the mechanical performance of concrete-filled spiral welded stainless steel tubes will be numerically investigated with a commercial finite element software package, through which an experimental program can be designed properly. Specifically, the proposed finite element models take into account the effects of material and geometric nonlinearities. Moreover, the initial imperfections of stainless steel tubes and the form of helical welding will be appropriately included. Enhancement of the understanding of the analysis results can be achieved by extending results through a series of parametric studies based on the developed finite element model. Thus, the effects of various design parameters will be further evaluated by using the developed finite element model. Furthermore, for the purposes of wide application of such types of structure, the accuracy of the behaviour prediction in terms of ultimate strength based on current design codes will be studied. The authors herein compared the load capacity between the finite element analysis results and the existing codes of practice.
Second-order flexibility-based model for nonlinear inelastic analysis of composite steel-concrete frameworks with partial composite action and semi-rigid connections
Authors: Chiorean Cosmin G , Buru Marius S
Published: July 2018

This paper presents an efficient computer method for large deflection distributed plasticity analysis of 3D semi-rigid composite steel-concrete frameworks. A novel second-order inelastic flexibility-based element has been developed by combining the Maxwell-Mohr rule and the second-order force based functions for computation of the generalized displacements. The proposed model allows explicit and efficient modeling of the combined effects of nonlinear geometrical effects, gradual spread-of-plasticity, partial shear connection of composite beams, finite-size joints and joint flexibility by using only one 2-noded beam-column element per physical member. For composite beams, based on elasto-plastic cross-sectional analyses the model is able to take into account the effects of partial composite action between the concrete slab and the steel beam. At the cross-sectional level the proposed method addresses computational efficiency through the use of path integral approach to numerical integration of the cross-sectional nonlinear characteristics and residual stresses, enabling in this way the accurate geometrical specifications and precise modeling of cross-sections. The proposed nonlinear analysis formulation has been implemented in a general nonlinear static purpose computer program, NEFCAD. Several computational examples are given to validate the accuracy and efficiency of the proposed method.
Second-order Direct Analysis of Steel Structures made of tapered members
Authors: Chan Siu-lai , Liu SW , Liu YP
Published: July 2018

Mild steel hot-rolled sections are commonly prismatic because of the rolling process with a furnace, but welded sections made from steel plates do not have such a constraint, especially when robotic welding machines are used. The weight saving could be very significant by, say, using wide flanged section at mid-span and a small flanged section at ends of a simply supported beam. However, design codes do not provide formulae for buckling check of tapered members. This paper proposes a code-free second-order direct analysis for stabilty design of steel frames made of tapered members. The design is further applied to a single layered mega space frame of 136m span. In the whole design process based on the concept of Second-order Direct Analysis, no uncertain effective length and independent member buckling checking are required.