# Shear Behavior of Concrete Encased Steel Truss Composite Girders  
[PERSON]  
1 Korea Authority of Land & Infrastructure Safety 24, Ena-ro 128 beon-gil, Jinju-si 52856, Korea; [EMAIL_ADDRESS]  
[PERSON]  
2 Department of Architectural Engineering, University of Seoul, 163 Seoulisripdae-ro, Dongdaemun-gu, Seoul 02504, Korea; [EMAIL_ADDRESS] (S-H.C.); [EMAIL_ADDRESS] (S-J.H.) [PERSON]  
3 Sejin R&S 19, Seongsuil-ro, Seongdong-gu, Seoul 04779, Korea; [EMAIL_ADDRESS] 3  
[PERSON]  
2 Department of Architectural Engineering, University of Seoul, 163 Seoulisripdae-ro, Dongdaemun-gu, Seoul 02504, Korea; [EMAIL_ADDRESS] (S-J.H.) [PERSON]  
4 School of Architecture & Architectural Engineering, Hanyang University, Erica 55 Hanyangdaehak-ro, Sangrok-gu, Ansan 15858, Korea; [EMAIL_ADDRESS]  
[PERSON]  
5 Department of Architectural Engineering and Smart City Interdisciplinary Major Program, University of Seoul, 163 Seoulisripdae-ro, Dongdaemun-gu, Seoul 02504, Korea; [EMAIL_ADDRESS]; Tel: +82-2-6490-2762; Fax: +82-2-6490-55095  
fiber reinforced polymer (GFRP) girders--in which various types of connections were set as key variables--to identify the bond performance between GFRP girders and concrete slabs. Based on the test results, [PERSON] et al. reported that the use of connections with single T-shaped and slotted perforated plates resulted in high load-carrying capacity and that the transverse rebar could enhance the ultimate bearing capacity and ductility. [PERSON] et al. [18] proposed a method for finite element modeling of the dynamic properties of steel-polymer concrete beams, and their model showed a good accuracy in the evaluation of the natural frequencies and mode shapes obtained from their experiments. Meanwhile, although studies regarding composite members have actively been conducted in recent years, the demand for a composite structural system demonstrating excellent structural performance while ensuring economic feasibility and constructability is still prevalent in the construction market. Accordingly, in South Korea, encased steel truss (EST) composite girders with steel trusses embedded in concrete have been developed recently, as shown in Figure 1. In the EST composite system, the truss member supports the formwork self-weight and construction load, thereby minimizing temporary work processes, such as shore installation. Figure 1a shows the EST composite girder. The steel truss fabricated in a plant comprises top and bottom chords as well as transverse and diagonal members. Furthermore, the truss and external formwork are installed at the site. After cast-in-place (CIP) concrete is poured and cured, grout is injected into the truss connection, as shown in Figure 1b. Figure 2 shows the connection details of the EST composite system. The bolt hole with a diameter of 18 mm was drilled at the end of the truss members and penetrated through a screw rod of 15.9 mm in diameter and 400 MPa yield strength; subsequently, the chord and diagonal members were fastened together using D-corn and bolts. The D-corns, which served as a spacer between the diagonal members and the form, were removed after the concrete was poured and cured, and subsequently the remaining space was filled with mortar. In the EST composite girder, an efficient load transfer was possible because the top and bottom chords of the truss resisted compressive and tensile forces due to bending moments, whereas the transverse and diagonal members as well as concrete resisted shear forces. The aim of this study was to verify the shear performance of the EST composite girder. Hence, the truss type (Pratt truss and Warren truss) and presence of stirrups were set as the main test variables, and shear tests were performed subsequently. The crack patterns and shear-force-displacement behaviors of the specimens were analyzed in detail.