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CONTENTS
Volume 23, Number 4, March20 2017
 

Abstract
Currently, CFRP (Carbon Fiber Reinforced Polymer) plate bonding is used quite extensively as a strengthening method. In this technique, a composite CFRP plate or sheet of relatively small thickness is bonded with an adhesion material to steel or concrete structure in order to improve its structural behavior and strength. The sheets or plates do not require much space and give a composite action between the adherents. In this study, the rotation capacity of CFRP-strengthened cold-formed steel (CFS) beams has been evaluated through numerical investigation. Studies on different structural levels have been performed. At the beam level, C-section has been adopted with different values of profile thickness, web height, and flange width. At the connection level, a web bolted moment resistant type of connection using through plate has been adopted. In web-bolted connections without CFRP strengthening, premature web buckling results in early loss of strength. Hence, CFRP sheets and plates with different mechanical properties and geometric configurations have been examined to delay web and flange buckling and to produce relatively high moment strength and rotation capacity. The numerical results reveal that CFRP strengthening may increase strength, initial stiffness, and rotation capacity when compared with the case without strengthening.

Key Words
cold-formed steel beam; rotation capacity; through plate moment connection; carbon fiber reinforced polymer; strengthening

Address
Department of Structural Engineering, Faculty of Engineering, Cairo University, Egypt.

Abstract
This paper experimentally studies the cyclic behavior of hybrid connections between steel coupling beams and concrete shear walls with embedded steel columns. Four beam-to-wall connection specimens with short and long embedded steel columns are tested under monotonic and cyclic loads, respectively. The influence of embedment length of columns on the failure mode and performance of connections is investigated. The results show that the length of embedded steel columns has significant effect on the failure mode of connections. A connection with a long embedded column has a better stiffness, loadbearing capacity and ductility than that of a short embedded column. The former fails due to the shear yielding of column web in the joint panel, while failure of the latter is initiated by the yielding of horizontal reinforcement in the wall due to the rigid rotation of the column. It is recommended that embedded steel columns should be placed along the entire height of shear walls to facilitate construction and enhance the ductility.

Key Words
steel coupling beam; beam-to-wall connection; embedded steel column; failure mode; load-bearing capacity

Address
(1) Guo-Qiang Li, Jian Jiang, Feifei Sun:
State Key Laboratory for Disaster Reduction in Civil Engineering, Tongji University, Shanghai 200092, China;
(2) Fulin Gu:
College of Civil Engineering, Tongji University, Shanghai 200092, China.

Abstract
This paper theoretically studies the cyclic behavior of hybrid connections between steel coupling beams and concrete shear walls with embedded steel columns. Finite element models of connections with long and short embedded steel columns are built in ABAQUS and validated against the test results in the companion paper. Parametric studies are carried out using the validated FE model to determine the key influencing factors on the load-bearing capacity of connections. A close-form solution of the load-bearing capacity of connections is proposed by considering the contributions from the compressive strength of concrete at the interface between the embedded beam and concrete, shear yielding of column web in the tensile region, and shear capacity of column web and concrete in joint zone. The results show that the bond slip between embedded steel members and concrete should be considered which can be simulated by defining contact boundary conditions. It is found that the load-bearing capacity of connections strongly depends on the section height, flange width and web thickness of the embedded column. The accuracy of the proposed calculation method is validated against test results and also verified against FE results (with differences within 10%). It is recommended that embedded steel columns should be placed along the entire height of shear walls to facilitate construction and enhance the ductility. The thickness and section height of embedded columns should be increased to enhance the load-bearing capacity of connections. The stirrups in the joint zone should be strengthened and embedded columns with very small section height should be avoided.

Key Words
steel coupling beam; beam-to-wall connection; embedded steel column; failure mode; load-bearing capacity; close-form solution

Address
(1) Guo-Qiang Li, Jian Jiang, Feifei Sun:
State Key Laboratory for Disaster Reduction in Civil Engineering, Tongji University, Shanghai 200092, China;
(2) Fulin Gu:
College of Civil Engineering, Tongji University, Shanghai 200092, China.

Abstract
Experimental and numerical studies of a newly developed Reduced Beam Section (RBS) connection, called Tubular Web RBS connection (TW-RBS) have been recently conducted. This paper presents experimental and numerical results of extending the plastic hinge length on the beam flange to increase energy dissipation of a proposed version of the TW-RBS connection with two pipes, (TW-RBS(II)), made by replacing a part of flat web with two steel tubular web at the desirable location of the beam plastic hinge. Two deep-beam specimens with two pipes are prepared and tested under cyclic loads. Obtained results reveal that the TW-RBS(II) like its type I, increases story drift capacity up to 6% in deep beam much more than that stipulated by the current seismic codes. Based on test results, the proposed TW-RBS(II) helps to dissipate imposed energy up to 30% more than that of the TW-RBS(I) specimens at the same story drift and also reduces demands at the beam-to-column connection up to 30% by increasing plastic hinge length on the beam flange. The TW-RBS(II) specimens are finally simulated using finite element method showing good agreement with experimental results.

Key Words
energy dissipation; plastic hinge length; reduced beam section; accordion web RBS; two pipes; accordion cells

Address
(1) Seyed M. Zahrai, Seyed R. Mirghaderi:
School of Civil Engineering, College of Engineering, The University of Tehran, Iran;
(2) Aboozar Saleh:
Department of Civil Engineering, Islamic Azad University Professor Hesabi Branch, Tafresh, Iran.

Abstract
In the past, the progressive collapse resulting from local failures during accidents has caused many tragedies and loss of life. Although long-span spatial grid structures are characterised by a high degree of static indeterminacy, the sudden failure of key members may lead to a catastrophic progressive collapse. For this reason, it is especially necessary to research the progressive collapse resistance capacity of long-span spatial grid structures. This paper presents an evaluation method of important members and a novel dynamic analysis method for simulating the progressive collapse of long-span spatial grid structures. Engineering cases were analysed to validate these proposed method. These proposed methods were eventually implemented in the progressive collapse analysis of the main stadium for the Universiade Sports Center. The roof of the structure was concluded to have good resistance against progressive collapse. The novel methods provide results close to practice and are especially suitable for the progressive collapse analysis of long-span spatial grid structures.

Key Words
long-span spatial grid structures; progressive collapse; multiple responses; analysis method; construction effect

Address
School of Civil Engineering, Xi'an University of Architecture and Technology, Xi'an 710055, P.R. China.

Abstract
This study intends to improve the structural details of the anchors in the conventional CFT column-to-foundation connection. To that goal, finite element analysis is conducted with various design variables (number and embedded length of deformed bars, number, aspect ratio, height ratio and thickness ratio of ribs) selected based upon the results of loading test and strength evaluation. The finite element analysis is performed using ABAQUS and the analytical results are validated by comparison with the load-displacement curves obtained through loading test applying axial and transverse loads. The behavioral characteristics of the numerical model according to the selected design variables are verified and the corresponding results are evaluated.

Key Words
CFT column-to-foundation; finite element analysis; anchors; deformed bars; ribs

Address
(1) Hee-Ju Kim:
Construction R&D Department, Korea Agency for infrastructure Technology Advancement, 286 simin-Daero, Dongan, Anyang-si, Gyeonggi, 14066, Korea;
(2) Junsu Ham, Won-Sup Hwang:
Department of Civil Engineering, Inha University, 100 Inha-ro, Nam-gu, Incheon 22212, Republic of Korea;
(3) Ki-Tae Park:
Structural Engineering Research Institute, Korea Institute of Civil Engineering and Building Technology, 283 Goyangde-ro, Ilsanseo-gu, Goyang-si, Gyeonggi-do, 10223 Republic of Korea.

Abstract
The square tubed-reinforced concrete (TRC) column is a kind of special concrete-filled steel tube (CFST) columns, in which the outer thin-walled steel tube does not pass through the beam-column joint, so that the longitudinal steel reinforcing bars in the RC beam are continuous through the connection zone. However, there is a possible decrease of the axial bearing capacity at the TRC column to RC beam connection due to the discontinuity of the column tube, which is a concern to engineers. 24 connections and 7 square TRC columns were tested under axial compression. The primary parameters considered in the tests are: (1) connection location (corner, exterior and interior); (2) dimensions of RC beam cross section; (3) RC beam type (with or without horizontal haunches); (4) tube type (with or without stiffening ribs). The test results show that all specimens have relatively high load-carrying capacity and satisfactory ductility. With a proper design, the connections exhibit higher axial resistance and better ductility performance than the TRC column. The feasibility of this type of connections is verified.

Key Words
square tubed-reinforced-concrete (TRC); concrete filled tube connections; horizontal haunched RC beam; failure pattern; axial compression behavior

Address
(1) Xu-Hong Zhou, Bin-Yang Li, Dan Gan, Jie-Peng Liu:
Key Laboratory of New Technology for Construction of Cities in Mountain Area (Ministry of Education), Chongqing University, Chongqing 400045, China;
(2) Xu-Hong Zhou, Bin-Yang Li, Dan Gan, Jie-Peng Liu:
School of Civil Engineering, Chongqing University, Chongqing, 40045, China;
(3) Dan Gan:
School of Civil Engineering, Chang'an University, Xi'an 710061, China;
(4) Y. Frank Chen:
Department of Civil Engineering, The Pennsylvania State University, Middletown, PA 17057, USA.

Abstract
This paper presents an experimental study, investigating the compressive behavior of glass-fibre reinforced and unreinforced cementitious material-filled square steel tubular (GFCMFST and CMFST) columns. The specimens were manufactured by using high performance cementitious materials without using coarse aggregate. The influence of adding glassfibres to the mix on the behavior of both axially and eccentrically loaded columns is considered. It was found that adding glass fibre improvesthe confinement behavior, the axial compressive strength, the stiffness and the toughness of both axially and eccentrically loaded columns. The compressive strength of axially loaded columns is compared with strength predictions according to EC4 and the AISC specification. It was found that the design predictions according to EC4 and the AISC codes provide conservative results for CMFST and GFCMFST columns. Alternatively, the axial load.bending moment interaction diagrams specified in theEC4 are conservative for the eccentrically tubular CMFST and GFCMFST tested columns.

Key Words
experimental investigation; cementitious material-filled; square hollow section; glass-fibre; axially loaded column; eccentrically loaded column

Address
Department of Structural Engineering, Faculty of Engineering, Tanta University, Tanta, Egypt.

Abstract
Steel plate shear wall (SPSW) system has been increasingly used for lateral loads resisting system since 1980s when the utilization of post-buckling strength of SPSW was realized. The structural response of SPSWs largely depends on the behavior of the surrounded beams. The beams are normally required to behave in the elastic region when the SPSW fully buckled and formed the tension field action. However, most modern design codes do not specify how this requirement can be achieved. This paper presents theoretical investigation and design procedures of manually calculating the plastic flexural capacity of the beams of SPSWs and can be considered as an extension to the previous work by Qu and Bruneau (2011). The reduction in the plastic flexural capacity of beam was considered to account for the presence of shear stress that was altered towards flanges at the boundary region, which can be explained by Saint-Venant

Key Words
steel plate shear wall; beam; flexural behavior; Saint-Venant's principle; capacity

Address
Key Laboratory of Concrete and Prestressed Concrete Structures of the Ministry of Education, Southeast University, Nanjing, China.

Abstract
This paper presents an experimental study on the behavior of concrete-encased composite columns with multi-separate steel sections subjected to axial and eccentric loads. Six 1/4-scaled concrete-encased composite columns were tested under static loads. The specimens were identical in geometric dimensions and configurations, and the parameter of this experiment was the eccentricity ratio of the applied load. Each two of the specimens were loaded with 0, 10%, and 15% eccentricity ratios. The capacity, deformation pattern, and failure mode of the specimens were carefully examined. Test results indicate that full composite action between the concrete and the steel sections can be realized even though the steel sections do not connect with one another. The concrete-encased composite columns can develop stable behavior and sufficient deformation capacity by providing enough transverse reinforcing bars. Capacities of the specimens were evaluated based on both the Plain Section Assumption (PSA) method and the superimposition method. Results show that U.S. and Chinese codes can be accurate and safe in terms of bending capacities. Test results also indicate that the ACI 318 and Mirza methods give the best predictions on the flexural stiffness of this kind of composite columns.

Key Words
static test; concrete-encased composite column; separate steel sections; capacity; stiffness

Address
(1) Congzhen Xiao, Tao Chen:
China Academy of Building Research, 30 Beisanhuandong Lu, Beijing, China;
(2) Fei Deng, Zuozhou Zhao:
Department of Civil Engineering, Tsinghua University, 30 Shuangqing Lu, Beijing, China.


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