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Volume 23, Number 2, February10 2017

This paper focuses on the seismic performance of pallet-type steel storage rack structures in their down aisle direction. As evidenced by experimental research, the seismic response of storage racks in the down-aisle direction is strongly affected by the nonlinear moment-rotation response of the beam-to-column connections. In their down-aisle direction, rack structures are designed to resist lateral seismic loads with typical moment frames utilizing proprietary beam-to-column moment- resisting connections. These connections are mostly boltless hooked type connections and they exhibit significantly large rotations resulting in large lateral frame displacements when subjected to strong ground motions. In this paper, typical hooked boltless beam-to-column connections are studied experimentally to obtain their non-linear reversed cyclic moment-rotation response. Additionally, a compound type connection involving the standard hooks and additional bolts were also tested under similar conditions. The simple introduction of the additional bolts within the hooked connection is considered to be a practical way of structural upgrade in the connection. The experimentally evaluated characteristics of the connections are compared in terms of some important performance indicators such as maximum moment and rotation capacity, change in stiffness and accumulated energy levels within the cyclic loading protocol. Finally, the obtained characteristics were used to carry out seismic performance assessment of rack frames incorporating the tested beam-to-column connections. The assessment involves a displacement based approach that utilizes a simple analytical model that captures the seismic behavior of racks in their down-aisle direction. The results of the study indicate that the proposed method of upgrading appears to be a very practical and effective way of increasing the seismic performance of hooked connections and hence the rack frames in their down-aisle direction.

Key Words
steel storage rack; hooked connection; cyclic test; seismic performance; structural upgrade

(1) Bassel El Kadi, Atakan Mang

It is extremely important to be aware of the ballistic performances of engineering materials in order to be able to choose the lightest armor providing full ballistic protection in civil and military applications. Therefore, ballistic tests are an important part of armor design process. In this study, ballistic performance of plates made of carbon steel and cold worked tool steel against 7.62 mm AP (armor-piercing) bullets was examined experimentally and numerically in accordance with NIJ standards. Samples in different sizes were prepared to demonstrate the effect of target thickness on ballistic performance. Some of these samples were coated with titanium nitride using physical vapor deposition (PVD) method. After examining all successful and unsuccessful samples at macro and micro levels, factors affecting ballistic performance were determined. Explicit non-linear analyses were made using Ls-Dyna software in order to confirm physical ballistic test results. It was observed that the ballistic features of steel plates used in simulations comply with actual physical test results.

Key Words
ballistic performance; Titanium Nitride (TiN); bullet impact; explicit non-linear analysis

(1) Erdi Ergül, Murat Pakdil:
Abant Izzet Baysal University, Department of Mechanical Engineering, 14280, Bolu, Turkey;
(2) Emre Doruk:
TOFAS-FIAT, R&D Department, 16369, Bursa, Turkey;
(3) Emre Doruk:
Sakarya University, Department of Manufacturing Engineering, 54187, Sakarya, Turkey.

A new composite tube connection method called the pre-tightened teeth connection technique is proposed to improve the composite tube connection efficiency. This paper first introduces the manufacturing process of the proposed technique. It then outlines how the mechanical properties of this technology were tested using four test groups. The factors that influence the load-bearing capacity and damage model of the connection were analyzed, and finally, the transfer load mechanism was investigated. The following conclusions can be obtained from the research results. (1) The new technique improves the compressive connection efficiency by a maximum of 79%, with the efficiency exceeding that of adhesive connections of the same thickness. (2) Changing the depth of teeth results in two types of damage: local compressive damage and shear damage. The bearing capacity can be improved by increasing the depth, length, and number of teeth as well as the pretightening force. (3) The capacity of the technique to transfer high loads is a result of both the relatively high interlaminar shear strength of the pultruded composite and the interlaminar shear strength increase provided by the pre-tightening force. The proposed technique shows favorable mechanical properties, and therefore, it can be extensively applied in the engineering field.

Key Words
composite tube; pre-tightened teeth connection; connection efficiency; influence factors

(1) Fei Li:
Institute of Logistics Engineering of PLA, Chongqing 400000, China;
(2) Qilin Zhao:
School of Mechanical and Power Engineering, Nanjing University of Technology, Nanjing 21007, China;
(3) Haosen Chen:
Institute of Advanced Structure Technology, Beijing Institute of Technology, Beijing 100081, China;
(4) Longxing Xu:
The First Research Division, General Equipment Department of the PLA, Wuxi 214035, China.

Conceptual configuration and seismic performance of high-rise steel frame-brace structure are studied. First, the topology optimization problem of minimum volume based on truss-like material model under earthquake action is presented, which is solved by full-stress method. Further, conceptual configurations of 20-storey and 40-storey steel frame-brace structure are formed. Next, the 40-storeystructure model is developed in Opensees. Two common configurations are utilized for comparison. Last, seismic performance of 40-storey structure is derived using nonlinear static analysis and nonlinear dynamic analysis. Results indicate that structural lateral stiffness and maximum roof displacement can be improved using brace. Meanwhile seismic damage can also be decreased. Moreover, frame-brace structure using topology optimization is most favorable to enhance lateral stiffness and mitigate seismic damage. Thus, topology optimization is an available way to form initial conceptual configuration in high-rise steel frame-brace structure.

Key Words
brace; topology optimization; seismic performance; incremental dynamic analysis; high-rise steel frame; pushover

(1) Shengfang Qiao, Xiaolei Han, Weichen Li:
School of Civil Engineering and Transportation, South China University of Technology, Tianhe, Guangzhou, 510641, China;
(2) Kemin Zhou:
College of Civil Engineering, Huaqiao University, Jimei, Xiamen, 361021, China.

To reuse a broken plain concrete (PC) arch, a retrofitting method was proposed to ensure excellent structural performances, in which carbon fiber reinforced polymers (CFRPs) were applied to repair and strengthen the damaged PC arch through bonding and wrapping techniques. Experiments were carried out to reveal the deformation and the load carrying capacity of the retrofitted composite arch. Based on the experiments, repairing and strengthening effects of the CFRP retrofitted broken arch were revealed. Simplified analysing model was suggested to predict the peak load of the CFRP retrofitted broken arch. According to the research, it is confirmed that absolutely broken PC arch can be completely repaired and reinforced, and even behaves more excellent than the intact PC arch when bonded together and strengthened with CFRP sheets. Using CFRP bonding/wrapping technique a novel efficient composite PC arch structure can be constructed, the comparison between rebar reinforced concrete (RC) arch and composite PC arch reveals that CFRP reinforcements can replace the function of steel bars in concrete arch.

Key Words
composite structures; failure/failure mode; fiber reinforced polymers (FRP); structural analysis

(1) Peng Wang, Meirong Jiang, Hailong Chen, Fengnian Jin, Jiannan Zhou:
State Key Laboratory of Disaster Prevention & Mitigation of Explosion & Impact, PLA University of Science and Technology, Nanjing, China;
(2) Hualin Fan:
Research Center of Lightweight Structures and Intelligent Manufacturing, State Key Laboratory of Mechanics and Control of Mechanical Structures, Nanjing University of Aeronautics and Astronautics, Nanjing, China;
(3) Peng Wang, Qing Zheng, Hualin Fan:
State Key Laboratory of Constructional Machinery, Zoomlion Heavy Industry Science & Technology Co., Ltd., Changsha, China.

The effects of plaster on the behavior of single-story single-bay masonry-infilled steel frames under in-plane base accelerations have been experimentally investigated by a shake-table. Tested structures were made in a 1/3 scale, with realistic material properties and construction methods. Steel frames with high and low flexural rigidity of beams and columns were considered. Each type of frame was tested with three variants of masonry: (i) non-plastered masonry; (ii) masonry infill with conventional plaster on both sides; and (iii) masonry infill with a polyvinyl chloride (PVC) net reinforced plaster on both sides. Masonry bricks were made of lightweight cellular concrete. Each frame was firstly successively exposed to horizontal base accelerations of an artificial accelerogram, and afterwards, to horizontal base accelerations of a real earthquake. Characteristic displacements, strains and cracks in the masonry were established for each applied excitation. It has been concluded that plaster strengthens the infill and prevents damages in it, which results in more favorable behavior and increased bearing capacity of plastered masonry-infilled frames compared to non-plastered masonry-infilled frames. The load-bearing contribution of the adopted PVC net in the plaster was not noticeable for the tested specimens, probably due to relative small cross section area of fibers in the net. Behavior of masonry-infilled steel frames significantly depends on frame stiffness. Strong frames have smaller displacements than weak frames, which reduces deformations and damages of an infill.

Key Words
masonry-infilled frame; plaster; fiber-reinforcement; shake-table; earthquake

Faculty of Civil Engineering, Architecture and Geodesy, University of Split, Matice hrvatske 15, 21000 Split, Republic of Croatia.

The use of advanced fibre composite materials in bridge engineering offers alternative solutions to structural problems compared to traditional construction materials. Advanced composite or fibre reinforced polymer (FRP) materials have high strength to weight ratios, which can be especially beneficial where dead load or material handling considerations govern a design. However, the reduced weight and stiffness of FRP footbridges results in generally poorer dynamic performance, and vibration serviceability is likely to govern their design to avoid the footbridge being "too lively". This study investigates the dynamic behaviour of the 51.3 m span Wilcott FRP suspension footbridge. The assessment is performed through a combination of field testing and finite element analysis, and the measured performance of the bridge is being used to calibrate the model through an updating procedure. The resulting updated model allowed detailed interpretation of the results. It showed that non-structural members such as the parapets can influence the dynamic behaviour of slender, lightweight footbridges, and consequently their contribution must be included during the dynamic assessment of a structure. The test data showed that the FRP footbridge is prone to pedestrian induced vibrations, although the measured response levels were lower than limits specified in relevant standards.

Key Words
fibre reinforced polymer; footbridges; vibration serviceability; finite element method; dynamic test

(1) Renos A. Votsis, Elia A. Tantele:
Department of Civil Engineering and Geomatics, Cyprus University of Technology, Saripolou street 2-8, Achilleos Building 1, Floor 1, 3603 Limassol, Cyprus;
(2) Tim J. Stratford:
School of Engineering, University of Edinburgh, UK;
(3) Marios K. Chryssanthopoulos:
Civil Engineering (C5), Faculty of Engineering and Physical Sciences, University of Surrey, UK.

Braces are one of the retrofitting systems of structure under earthquake loading. Buckling restrained braces (BRBs) are one of the very efficient braces for lateral loads. One of the key needs for a desirable and acceptable behavior of bucklingrestraining brace members under intensive loading is that it prevents total buckling until the bracing member tolerates enough plastic deformation and ductility. This paper presents the results of a set of analysis by finite element method on buckling restrained braces in which the filler materials within the restraining member have been removed. These braces contain core as the conventional BRBs, but they have a different buckling restrained system. The purpose of this analysis is conducting a parametric study on various empty spaces between core and restraining member, the effect of friction between core and restraining member and applying initial deformation to brace system to investigate the global buckling behavior of these braces. The results of analysis indicate that the flexural stiffness of restraining member, regardless of the amount of empty space, can influence the global buckling behavior of brace significantly.

Key Words
buckling restrained brace (BRB); finite element method; cyclic loading; global buckling

(1) Seyed Masoud Mirtaheri:
Department of Civil Engineering, K.N. Toosi University of Technology, Tehran, Iran;
(2) Meissam Nazeryan:
Department of Civil Engineering, Sharif University of Technology, Tehran, Iran;
(3) Mohammad Kazem Bahrani, Amin Nooralizadeh:
Department of Civil Engineering, University of Qom, Qom, Iran;
(4) Leila Montazerian:
Department of Civil Engineering, Chalus Branch, Islamic Azad University, Chalus, Iran;
(5) Mohamadhosein Naserifard:
Department of Civil Engineering, Yazd Branch, Islamic Azad University, Yazd, Iran.

This paper presents a combined numerical and theoretical study on the composite action between steel and concrete of circular steel tube confined concrete (STCC) stub columns under axial compressive loading with a full theoretical elasto-plastic model and finite element (FE) model in comparison with experimental results. Based on continuum mechanics, the elasto-plastic model for STCC stub columns was established and the analysis was realized by a FORTRAN program and the three dimensional FE model was developed using ABAQUS. The steel ratio of the circular STCC columns were defined in range of 0.5% to 2% to analyze the composite action between steel tube and concrete, and make a further study on the advantages of the circular STCC columns. By comparing the results using the elasto-plastic methods with the parametric analysis result of FE model, the appropriate friction coefficient between the steel tube and core concrete was defined as 0.4 to 0.6. Based on ultimate balance theory, the formula of ultimate load capacity applying to the circular STCC stub columns was developed.

Key Words
circular steel tube; confinement; composite action; stress-strain relationship; elasto-plastic methods; ABAQUS

(1) Fa-xing Ding, Liu Tan, Liping Wang:
School of Civil Engineering, Central South University, Changsha, Hunan Province, 410075, P.R. China;
(2) Xue-mei Liu:
School of Civil Engineering and Built Environment, Queensland University of Technology, Brisbane, QLD 4000, Australia.

In the concept of two-parameter fatigue failure criterion, the material fatigue failure is determined by the damage degree and the current stress level. Based on this viewpoint, a residual strength degradation model for stud shear connectors under fatigue loads is proposed in this study. First, existing residual strength degradation models and test data are summarized. Next, three series of 11 push-out specimen tests according to the standard push-out test method in Eurocode-4 are performed: the static strength test, the fatigue endurance test and the residual strength test. By introducing the "two-parameter fatigue failure criterion," a residual strength calculation model after cyclic loading is derived, considering the nonlinear fatigue damage and the current stress condition. The parameters are achieved by fitting the data from this study and some literature data. Finally, through verification using several literature reports, the results show that the model can better describe the strength degradation law of stud connectors.

Key Words
steel-concrete composite bridge; stud connector; fatigue; residual strength; two-parameter fatigue failure criterion

School of Transportation, Southeast University, Nanjing 210096, China.

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