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Volume 36, Number 4, August25 2020

Nowadays, in prefabricated composite construction, composite action between steel beam and concrete slab is often achieved with positioning of shear connectors in envisaged openings of concrete slabs. Prefabricated concrete slabs are used for composite steel-concrete buildings and bridges, both for the construction of new structures and for renovation of existing ones, significantly reducing construction time. Development of different types of shear connectors represent alternative solution to the traditionally used headed studs, considering their shear resistance, stiffness and ductility. New types of shear connectors tend to reduce the construction time and overall construction cost. Mechanically fastened shear connectors represent a viable alternative to headed studs, considering their fast installation process and shear resistance. X-HVB shear connectors are attached to the steel beam with two cartridge fired pins. The first step towards extensive implementation of X-HVB shear connectors in composite construction is to understand their behaviour through experimental investigation. Results of the push-out tests, in accordance to Eurocode 4, with X-HVB 110 shear connectors positioned in envisaged openings of prefabricated concrete slabs are presented in this paper. The experimental investigation comprised three different specimen\'s layout. Group arrangement of X-HVB shear connectors in envisaged openings included specimens with minimal recommended distances and specimens with reduced distances between connectors in both directions. Influence of different installation procedures on overall behaviour of the connection is presented, as well as the orientation of shear connectors relative to the shear force direction. Influence of variations is characterized in terms of failure mechanisms, shear resistance and ductility.

Key Words
X-HVB, experiments; cartridge fired pins; push-out test; steel-concrete composite structures

Nina Gluhovic, Zlatko Markovic and Milan Spremic: Department of Materials and Structures, Faculty of Civil Engineering University of Belgrade, B. k. Aleksandra 73, Serbia
Marko Pavlovic: Department of Engineering Structures, Faculty of Civil Engineering and Geosciences, Delft University of Technology,
Stevinweg 1, Delft, The Netherlands

This paper investigates the progressive collapse behavior of 3D steel-framed gravity buildings under fires with a cooling phase. The effect of fire protections and bracing systems on whether, how, and when a gravity building collapses is studied. It is found that whether a building collapses or not depends on the duration of the heating phase, and it may withstand a \"short-hot\" fire, but collapses under a mild fire or a \"long-cool\" fire. The collapse time can be conservatively determined by the time when the temperature of steel columns reaches a critical temperature of 550C. It is also found that the application of a higher level of fire protection may prevent the collapse of a building, but may also lead to its collapse in the cooling phase due to the delayed temperature increment in the heated members. The tensile membrane action in a heated slab can be resisted by a tensile ring around its perimeter or by tensile yielding lines extended to the edge of the frame. It is recommended for practical design that hat bracing systems should be arranged on the whole top floor, and a combination of perimeter and internal vertical bracing systems be used to mitigate the fire-induced collapse of gravity buildings. It is also suggested that beam-to-column connections should be designed to resist high tensile forces (up to yielding force) during the cooling phase of a fire.

Key Words
progressive collapse; gravity building; parametric fire; cooling phase; fire protection; bracing system

Jian Jiang, Wei Chen and Jihong Ye: Jiangsu Key Laboratory of Environmental Impact and Structural Safety in Engineering,
China University of Mining and Technology, Xuzhou 221116, China
Wenyu Caiand Guo-Qiang Li:College of Civil Engineering, Tongji University, Shanghai 200092, China

Responses of semi-rigid frames having different degrees of semi-rigidity obtained by the nonlinear static analysis (NSA) are evaluated at specific target displacements by comparing them with those obtained by the nonlinear time-history analysis (NTHA) for scaled earthquakes. The peak ground accelerations (PGA) of the earthquakes are scaled such that the obtained peak top story displacements match with the target displacements. Three different types of earthquakes are considered, namely, far-field and near-field earthquakes with directivity and fling-step effects. In order to make the study a comprehensive one, three degrees of semi-rigidity (one fully rigid and the other two semi-rigid), and two frames having different heights are considered. An ensemble of five-time histories of ground motion is included in each type of earthquake. A large number of responses are considered in the study. They include the peak top-story displacement, maximum inter-story drift ratio, peak base shear, total number of plastic hinges, and square root of sum of the squares (SRSS) of the maximum plastic hinge rotations. Results of the study indicate that the nonlinear static analysis provides a fairly good estimate of the peak values of top-story displacements, inter-story drift ratio (for shorter frame), peak base shear and number of plastic hinges; however, the SRSS of maximum plastic hinge rotations in semi-rigid frames are considerably more in the nonlinear static analysis as compared to the nonlinear time history analysis.

Key Words
NSA; NTHA; semi-rigid frame; near-field; far-field; seismic performance; target displacement

Vijay Sharma: Department of Civil Engineering, Malaviya National Institute of Technology Jaipur, JLN Marg, Jaipur 302017, India
Mahendra K. Shrimali, Shiv D. Bharti and Tushar K. Datta: National Centre for Disaster Mitigation and Management, Malaviya National Institute of Technology Jaipur,
JLN Marg Jaipur, 302017, India

Drilling processes in fiber-reinforced polymer composites are essential for the assembly and fabrication of composite structural parts. The economic impact of rejecting the drilled part is significant considering the associated loss when it reaches the assembly stage. Therefore, this article tends to illustrate the effect of cutting conditions (feed and speed), and laminate thickness on thrust force, torque, and delamination in drilling woven E-glass fiber reinforced epoxy (GFRE) composites. Four feeds (0.025, 0.05, 0.1, and 0.2 mm/r) and three speeds (400, 800, and 1600 RPM) are exploited to drill square specimens of 36.6x36.6 mm, by using CNC machine model \"Deckel Maho DMG DMC 1035 V, ecoline\". The composite laminates with thicknesses of 2.6 mm, 5.3 mm, and 7.7 mm are constructed respectively from 8, 16, and 24 glass fiber layers with a fiber volume fraction of about 40%. The drilled specimen is scanned using a high-resolution flatbed color scanner, then, the image is analyzed using CorelDraw software to evaluate the delamination factor. Multi-variable regression analysis is performed to present the significant coefficients and contribution of each variable on the thrust force and delamination. Results illustrate that the drilling parameters and laminate thickness have significant effects on thrust force, torque, and delamination factor.

Key Words
drilling of composite; woven glass fiber; thrust force and torque; delamination, Multiple Regression

Usama. A. Khashaba and Mohamed A Eltaher: Mechanical Engineering Department, Faculty of Engineering, King Abdulaziz University,
P.O. Box 80204, Jeddah 22254-2265, Saudi Arabia;
Mechanical Design and Production Engineering Department, Faculty of Engineering, Zagazig University, Egypt
Mohamed S. Abd-Elwahed, Khaled I. Ahmed,
Ismail Najjar, Ammar Melaibari: Mechanical Engineering Department, Faculty of Engineering, King Abdulaziz University,
P.O. Box 80204, Jeddah 22254-2265, Saudi Arabia

This paper carries out the progressive collapse analysis of stainless steel composite beam-to-column joint sub-models and moment-resisting frames under column removal scenarios. The static flexural response of composite joint sub-models with damaged columns was initially explored via finite element methods, which was validated by independent experimental results and discussed in terms of moment-rotation relationships, plastic hinge behaviour and catenary actions. Simplified finite element methods were then proposed and applied to the frame analysis which aimed to elaborate the progressive collapse response at the frame level. Nonlinear static and dynamic analysis were employed to evaluate the dynamic increase factor (DIF) for stainless steel composite frames. The results suggest that the catenary action effect plays an important role in preventing the damaged structure from dramatic collapse. The beam-to-column joints could be critical components that influence the capacity of composite frames and dominate the determination of dynamic increase factor. The current design guidance is non-conservative to provide proper DIF for stainless steel composite frames, and thus new DIF curves are expected to be proposed.

Key Words
progressive collapse; stainless steel; beam-to-column joints; static and dynamic; composite frames

Jia Wang, Brian Uy, Dongxu Li and Yuchen Song: School of Civil Engineering, The University of Sydney, Sydney, NSW, 2006, Australia

The paper aims to investigate the mechanical mechanism and seismic effect of stiffeners in blind bolt endplate connection to CFST column. A precise 3D finite element model with considering the cyclic properties of concrete and steel materials was established, and the efficiency was validated through monotonic and cyclic test data. The deforming pattern and the seismic performance of the unstiffened and stiffened blind bolt endplate connections were investigated. Then a parametric analysis was conducted to analyze the contribution of stiffeners and the joint working behaviors with endplate under cyclic load. The joint stiffness classifications were compared and a supplement stiffness classification method was proposed, and the energy dissipation ability of different class connections were compared and discussed. Results indicated that the main deformation pattern of unstiffened blind bolt endplate connections was the local bending of end plate. The vertical stiffeners can effectively alleviate the local bending deformation of end plate. And influence of stiffeners in thin endplate and thick endplate was different. Based on the stiffness of external diaphragm welded connection, a more detailed rigidity classification was proposed which included the pin, semi-rigid, quasi-rigid and rigid connection. Beam was the main energy dissipation source for rigid connection. For the semi-rigid and quasi-rigid connection, the extended endplate, stiffeners and steel beam would all participate in the energy dissipation.

Key Words
concrete filled steel tube (CFST); endplate connections; high-strength blind bolts; finite element (FE) analysis; energy dissipation; rigidity classification

Fa-xing Ding and Peng Liu: School of Civil Engineering, Central South University, Changsha, Hunan Province, 410075, PR China;
Engineering Technology Research Center for Prefabricated Construction Industrialization of Hunan Province, 410075, PR China
Zhi-cheng Pan and Shi-jian Huang: School of Civil Engineering, Central South University, Changsha, Hunan Province, 410075, PR China
Liang Luo: School of Civil Engineering and Architecture, Nanchang Hangkong University, Nanchang, Jiangxi Province, 330036, PR China
Tao Zhang: School of Civil Architecture, Zhengzhou University of Aeronautics, Zhengzhou, Henan Province, 450000, PR China

Although detailed shell analysis is suitable to predict the ductile crack initiation life of steel members, such detailed method adds time expense and complexity. In order to simply predict the ductile crack initiation life of stiffened steel bridge piers, a total of 33 cases are simulated to carry out the parametric analyses. In the analysis, the effects of the width-to-thickness ratio, slenderness ratio, plate thickness and so on are considered. Both shell analyses and beam analyses about these 33 cases are conducted. The plastic strain and damage index obtained from shell and beam analyses are compared. The modified factor Bs is determined based on the predicted results obtained from both shell and beam analyses in order to simulate the strain concentration at the base corner of the steel bridge piers. Finally, three experimental results are employed to verify the validity of the proposed method in this study.

Key Words
stiffened steel bridge pier; ductile crack initiation; evaluation method; cyclic loading

Wataru Fujie, Miki Taguchi and Hanbin Ge: Department of Civil Engineering, Meijo University, Nagoya 468-8502, Japan
Lan Kang: School of Civil Engineering and Transportation, South China University of Technology, Guangzhou, Guangdong Province,
510641, People\'s Republic of China;
State Key Laboratory of Subtropical Building Science, South China University of Technology, Guangzhou,
Guangdong Province, 510641, People\'s Republic of China
Bin Xu: College of Civil Engineering, Huaqiao University, Xiamen, Fujian 361021, People\' s Republic of China
Key Laboratory for Intelligent Infrastructure and Monitoring of Fujian Province
(Huaqiao University), Xiamen, Fujian 361021, People\'s Republic of China

To study the rail mapped deformation caused by the pier settlement of simply - supported bridges with China Railway Track System III (CRTS III) slab ballastless track (SBT) system under the mode of non-longitudinal connection ballastless track slab, this study derived an analytical solution to the mapped relationships between pier settlement and rail deformation based on the interlayer interaction mechanism of rail-pier and principle of stationary potential energy. The analytical calculation results were compared with the numerical results obtained by ANSYS finite element calculation, thus verifying the accuracy of analytical method. A parameter analysis was conducted on the key factors in rail mapped deformation such as pier settlement, fastener stiffness, and self-compacting concrete (SCC) stiffness of filling layer. The results indicate that rail deformation is approximately proportional to pier settlement. The smaller the fastener stiffness, the smoother the rail deformation curve and the longer the rail deformation area is. With the increase in the stiffness of SCC filling layer, the maximum positive deformation of rail gradually decreases, and the maximum negative deformation gradually increases. The deformation of rail caused by the pier settlement of common-span bridge structures will generate low-frequency excitation on high-speed trains.

Key Words
pier settlement; CRTS III SBT system; geometrical morphology of rail surface; mapped relationships; principle of stationary potential energy; subgrade

Lizhong Jiang:School of Civil Engineering, Central South University, Changsha 410075, China;
National Engineering Laboratory for High Speed Railway Construction, Changsha 410075, China
Lili Liu, Wangbao Zhou, Xiang Liu, Chao Liu and Ping Xiang:
School of Civil Engineering, Central South University, Changsha 410075, China

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