Advances in Structural Engineering

Lee, Jung-Han; Li, Chenghao; Oh, Sang-Hoon; Yang, Won-Jik; Yi, Waon-Ho

2008 Advances in Structural Engineering

doi: 10.1260/136943308786411998

The objectives of this study are to evaluate the variables that affect the shear behavior of unreinforced masonry (URM) walls and to propose the equation of the rocking and toe crushing strength of URM walls by regression analysis using the test data including the previous research. The main variables are the axial stress, the aspect ratio and the thickness of URM walls. The test results show that the specimens are governed by rocking and toe crushing failure modes. The relationship of the shear strength is proportionate to the square root of the vertical axial stress, and the relationship of the shear stress and aspect ratio is linearly proportional. Shear strength and cross sectional area are not proportional. For the URM walls tested, the proposed rocking and toe crushing strength/actual strength ratio of 0.95, and coefficient of correlation R of 0.9889 are more appropriate than the FEMA 306 rocking and toe crushing strength formulas.

Nagarajan, Praveen; Pillai, T. M. Madhavan

2008 Advances in Structural Engineering

doi: 10.1260/136943308786412050

Generally structural members can be broadly divided into two regions, namely B or Bernoulli regions where the strain distributions are linear and D or Disturbed regions where the strain distributions are nonlinear. A beam whose depth is comparable to span is known as deep beam and these structural elements belong to D regions. It has been recently understood that the strut and tie method (STM) is an effective tool for the design of both B and D regions. The present code recommendations are inadequate for the design of deep beams. In this paper simple equations using STM are developed for finding the area of main steel required to have a balanced type of failure and to find the ultimate capacity of deep beams failing in different failure modes. These equations are compared with experimental results and a good agreement is found.

Seyedpoor, S. M.; Gholizadeh, S.

2008 Advances in Structural Engineering

doi: 10.1260/136943308786412069

An efficient method is proposed to find optimal shape of arch dams subjected to response spectrum loading. The optimization is performed by a combination of simultaneous perturbation stochastic approximation (SPSA) and genetic algorithm (GA) methods. This new method is called simultaneous perturbation genetic algorithm (SPGA). Operation of SPGA includes three phases. In the first phase, a preliminary optimization is accomplished using SPSA. In the second phase, an optimal initial population is produced using the first phase results. In the last phase, GA is employed to find optimum design using the optimal initial population. The numerical results reveal the robustness and high performance of the proposed method for optimum shape design of arch dams. The optimum design obtained by SPGA is compared with those of SPSA and GA. It is demonstrated that the SPGA converges to better solution compared to SPSA and GA by spending lower computational cost.

Yao, George C.; Huang, Wen-Chun; Lin, Fan-Ru

2008 Advances in Structural Engineering

doi: 10.1260/136943308786412032

The performance of gap springs in a guideway sliding isolator (GSI) system developed to protect precision machinery against seismic motion has been studied. A spring is initially distanced from the system by a gap, causing the isolation system to exhibit nonlinear performance once the gap is closed, reducing the chance of resonance. A full-scale shaking table test of a 22-ton specimen and a numerical model simulation in SAP2000 have been performed. The study shows that springs possessing the appropriate gaps are more effective in controlling relative displacements than is a pure friction system. The optimal gap for a system subjected to far-field earthquakes was found to be 5mm. In addition, supplemental viscous damping of less than 15% of the critical damping had no significant effect on the GSI system far-field seismic response, but it did reduce the relative displacements of the system for near-fault seismic excitations.

Zhu, Feng; Zhao, Longmao; Lu, Guoxing; Wang, Zhihua

2008 Advances in Structural Engineering

doi: 10.1260/136943308786412005

This paper first presents an experimental investigation into the response of square sandwich panels with an aluminium foam core under blast loading, followed by a corresponding FE simulation using LS-DYNA. In the simulation, the loading process of explosive and response of the sandwich panels have been investigated. The blast loading process includes both the explosion procedure of the charge and interaction with the panel. The simulation result shows that the deformation/failure patterns observed in the tests are well captured by the numerical model, and quantitatively a reasonable agreement has been obtained between the simulation and experiment. Finally, a parametric study has been carried out to investigate the energy absorption performance of sandwich panels.

Nelson, Mark; Lai, Yu Ching; Fam, Amir

2008 Advances in Structural Engineering

doi: 10.1260/136943308786412023

A moment connection of concrete-filled fibre reinforced polymer (FRP) tubes (CFFTs) to concrete footing is explored. The CFFTs are directly embedded into the footings to develop their full moment capacity, in lieu of using mechanical connections, dowel reinforcing bars, or posttensioning methods. CFFT specimens of 219 mm diameter (D) were embedded into footings, at various depths, ranging from 0.3D to 1.5D. The CFFT cantilevered specimens were then laterally loaded to failure. The objective was to establish the critical embedment length, which was found to be 0.73D. Shorter embedment lengths resulted in a bond failure associated with excessive slip, where the full flexural strength of CFFTs was not reached. Specimens with the critical or longer embedment lengths have achieved flexural tension failure of the CFFT, just outside the footing. Ancillary push-through tests were also carried out using CFFT stubs embedded into concrete footings, throughout the full thickness of the footing, and tested under concentric compression loads. The objective was to establish the bond strength between the GFRP tube and concrete footing, which was found to be 0.75 MPa. The bond strength and critical embedment length will vary from case to case. As such, the parameters affecting their values have been identified.

Won, Jeong-Hun; Cho, Kwang-Il; Yoon, Ji-Hyun; Kim, Sang-Hyo

2008 Advances in Structural Engineering

doi: 10.1260/136943308786412041

This paper proposes an innovative key-segment closing method for partially earth-anchored cable-stayed bridges erected using free cantilever construction method, and examines its feasibility by performing a construction sequence analysis. The proposed method is based on the thermal prestressing technique, which gives an artificial heat to the girder in a cantilever state, in order to introduce the closing force required for connecting the key-segment to the adjacent segment by means of thermal expansion. The new method not only provides a feasible closing method for partially earth-anchored cable-stayed bridges, but also has a significant effect in reducing the axial force in the girders. A construction sequence analysis of an example bridge shows that the axial forces in the girders and the uplift forces at the bearings are reduced by a considerable amount due to application of the thermal prestressing method, whereas the member forces of cables and pylons are slightly changed. Therefore, it is verified from this study that the structural capacities of the girders and the bearings of the partially earth-anchored cable-stayed bridges can be effectively enhanced by application of the proposed method.

Park, Suhee; Choi, Sungmo; Park, Youngwook; Kim, Yosuk; Kim, Jinho

2008 Advances in Structural Engineering

doi: 10.1260/136943308786411989

This paper presents the development of an improved detail in partially restrained beam-to-column composite connections in concrete filled square tubes and the evaluation of its structural characteristics and behaviour under monotonic and cyclic loading. Studies for the bolted seat-angle connections of existing partially restrained composite connection (PR-CC) details have been conducted mostly on shallow beam-to-column connections. In case of deep beam-to-column connections, the fabrication becomes complicated because the sizes of the seat-angles are larger than the connections, and the number of bolts and welding length are increased. This study suggests a new detail of PR-CC which can be applied to concrete-filled tubular structures incorporating the effect of composite slabs and the performance for construction work. A welded bottom beam flange connection is proposed to enhance the capacity of the bottom of the connection and to improve ductility and fabrication. In addition, a reduced beam section (RBS) is adapted for the bottom beam flange to examine its effect on ductility. A seat-angle connection with penetrating bolts is also suggested and compared with the welded bottom beam flange connection. Both monotonic and cyclic loading tests are conducted on the five full scale specimens to compare and evaluate their ductility characteristics.

Seleem, H. El_Din H.; Shaheen, A. A. F.; Metwally, I. M.

2008 Advances in Structural Engineering

doi: 10.1260/136943308786412014

The present work is an experimental investigation concerned with developing plastering cement mortar characterized by an enhanced heat endurance to act as a heat barrier to rather sensitive materials like Advanced Composite Materials (ACM). For this purpose, finely ground waste glass and finely ground granulated blast furnace slag were introduced into the mortar mixtures. A total of eleven mixtures were cast, each of which comprises six groups of mortar cubes. For all mixtures, compressive strength is evaluated at ages extending from one week to three months. After 28 days of water curing, their compressive strengths were evaluated after exposure to elevated temperatures ranged from 200°C to 800°C. The retained strength after heat exposure is regarded as the heat endurance measure. A mineralogical study was conducted on the mortar specimens before and after exposure to 800°C. As a consequence, the formed cementitious phases and the heat induced transformations are clarified. Test results show that by utilizing either ground glass or ground slag a remarkable enhancement in strength and heat endurance can be achieved. This is due to their pozzolanic nature and superior thermal stability.