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CONTENTS
Volume 37, Number 1, January10 2011
 

Abstract
The response of concrete to transient dynamic loading has received extensive attention for both civil and military applications. Accordingly, thoroughly understanding the response and failure modes of concrete subjected to impact or explosive loading is vital to the protection provided by fortifications. Reactive powder concrete (RPC), as developed by Richard and Cheyrezy (1995) in recent years, is a unique mixture that is cured such that it has an ultra-high compressive strength. In this work, the concrete cylinders with different steel fiber volume fractions were subjected to repeated impact loading by a split Hopkinson Pressure Bar (SHPB) device. Experimental results indicate that the ability of repeated impact resistance of ultra-high-strength concrete was markedly superior to that of other specimens. Additionally, the rate of damage was decelerated and the energy absorption of ultra-high-strength concrete improved as the steel fiber volume fraction increased.

Key Words
steel fiber reinforced concrete; repeated impact; Hopkinson Pressure Bar test.

Address
Yuh-Shiou Tai: Department of Civil Engineering, ROC Military Academy, 1 Weiwu Rd, Fengshan, 830, Taiwan, ROC
Iau-Teh Wang: Department of Civil Engineering, ROC Military Academy, 1 Weiwu Rd, Fengshan, 830, Taiwan, ROC

Abstract
This paper presents a new Internet-based computational framework for the realistic simulation of multi-scale response of structural systems. Two levels of parallel processing are involved in this framework: multiple local distributed computing environments connected by the Internet to form a clusterto-cluster distributed computing environment. To utilize such a computing environment for a realistic simulation, the simulation task of a structural system has been separated into a simulation of a simplified global model in association with several detailed component models using various scales. These related multi-scale simulation tasks are distributed amongst clusters and connected to form a multi-level hierarchy. The Internet is used to coordinate geographically distributed simulation tasks. This paper also presents the development of a software framework that can support the multi-level hierarchical simulation approach, in a cluster-to-cluster distributed computing environment. The architectural design of the program also allows the integration of several multi-scale models to be clients and servers under a single platform. Such integration can combine geographically distributed computing resources to produce realistic simulations of structural systems.

Key Words
Internet computing; distributed processing; simulation; structural systems; hierarchical modeling.

Address
Hung-Ming Chen: Department of Construction Engineering, National Taiwan University of Science and Technology,
43, Sec. 4, Keelung Rd., Taipei 106, Taiwan
Yu-Chih Lin: Department of Construction Engineering, National Taiwan University of Science and Technology,
43, Sec. 4, Keelung Rd., Taipei 106, Taiwan

Abstract
Results of an experimental investigation on the behavior and ultimate shear capacity of 27 reinforced concrete Transfer (deep) beams are summarized. The main variables were percent longitudinal (tension) steel (0.28 to 0.60%), percent horizontal web steel (0.60 to 2.40%), percent vertical steel (0.50 to 2.25%), percent orthogonal web steel, shear span-to-depth ratio (1.10 to 3.20) and cube concrete compressive strength (32 MPa to 48 MPa).The span of the beam has been kept constant at 1000 mm with 100 mm overhang on either side of the supports. The result of this study shows that the load transfer capacity of transfer (deep) beam with distributed longitudinal reinforcement is increased significantly. Also, the vertical shear reinforcement is more effective than the horizontal reinforcement in increasing the shear capacity as well as to transform the brittle mode of failure in to the ductile mode of failure. It has been observed that the orthogonal web reinforcement is highly influencing parameter to generate the shear capacity of transfer beams as well as its failure modes. Moreover, the results from the experiments have been processed suitably and presented an analytical model for design of transfer beams in high-rise buildings for estimating the shear capacity of beams.

Key Words
shear resisting capacity; horizontal and vertical steel bars; shear span-to-depth ratio; national codes; transfer beam.

Address
R.S. Londhe: Government College of Engineering, Staion Road, Osmanpura, Aurangabad-431 005, India

Abstract
Static and dynamic responses of a completely free elastic beam resting on a two-parameter tensionless Pasternak foundation are investigated by assuming that the beam is symmetrically subjected to a uniformly distributed load and concentrated load at its middle. Governing equations of the problem are obtained and solved by paying attention on the boundary conditions of the problem including the concentrated edge foundation reaction in the case of complete contact and lift-off condition of the beam in a two-parameter foundation. The nonlinear governing equation of the problem is evaluated numerically by adopting an iterative procedure. Numerical results are presented in figures to demonstrate the non-linear behavior of the beam-foundation system for various values of the parameters of the problem comparatively by considering the static and dynamic loading cases.

Key Words
elastic beam; two-parameter foundation; lift-off.

Address
Z. Celep: Department of Structural and Earthquake Engineering, Faculty of Civil Engineering, Istanbul Technical University, 34469 Maslak, Istanbul, Turkey
K. Guler: Department of Structural and Earthquake Engineering, Faculty of Civil Engineering, Istanbul Technical University, 34469 Maslak, Istanbul, Turkey
F. Demir: Department of Civil Engineering, Faculty of Engineering, Suleyman Demirel University, 32260 Isparta, Turkey

Abstract
A simple mechanical model is proposed to demonstrate qualitatively the pancake progressive collapse of multi-storey structures. The impact between two collapsed storeys is simulated using a simple algorithm that builds on virtual mass-spring-damper system. To analyze various collapse modes, columns and beams are considered separately. Parametric studies show that the process of progressive collapse involves a large number of complex mechanisms. However, the proposed model provides a simple numerical tool to assess the overall behavior of collapse arising from a few initiating causes. Unique features, such as beam-to-beam connection failure criterion, and beam-to-column connection failure criterion are incorporated into the program. Besides, the criterion of local failure of structural members can also be easily incorporated into the proposed model.

Key Words
progressive collapse; impact; virtual spring; virtual damper.

Address
Weifeng Yuan: School of Civil and Environmental Engineering, Nanyang Technological University, 639798, Singapore
Kang Hai Tan: School of Civil and Environmental Engineering, Nanyang Technological University, 639798, Singapore

Abstract
This paper presents a tri-uniform bond stress model for predicting the lap splice strength of reinforcing bar at the critical bond splitting failure. The proposed bond distribution model consists of three zones, namely, splitting zone, post-splitting zone and yielding zone. In each zone, the bond stress is assumed to be constant. The models for bond strength in each zone are adopted from previous studies. Combining the equilibrium, strain-slip relation and the bond strength model in each zone, the steel stressslip model can be derived, which can be used in the nonlinear frame analysis of the column. The proposed model is applied to derive explicit equations for predicting the strength of the lap splice strengthened by fiber reinforced polymer (FRP) in both elastic and post-yield ranges. For design purpose, a procedure to calculate the required FRP thickness and the number of FRP sheets is also presented. A parametric investigation was conducted to study the relation between lap splice strength and lap splice length, number and thickness of FRP sheets and the ratio of concrete cover to bar diameter. The study shows that the lap splice strength can be enhanced by increasing one of these parameters: lap splice length, number or thickness of FRP sheets and concrete cover to bar diameter ratio. Verification of the model has been conducted using experimental data available in literature.

Key Words
confinement; lap splice strength; tri-uniform bond stress model; fiber-reinforced polymer; splitting failure.

Address
Dam Xuan Thai: Civil Engineering Department, The National University of Civil Engineering, Hanoi, VietnamAmorn Pimanmas: Sirindhorn International Institute of Technology, Thammasat University, Pathum Thani 12121, Thailand

Abstract
This paper presents a nonlinear analysis of reinforced concrete column with lap splice confined by FRP wrapping in the critical hinging zone. The steel stress-slip model derived from the triuniform bond stress model presented in the companion paper is included in the nonlinear frame analysis to simulate the response of reinforced concrete columns subjected to cyclic displacement reversals. The nonlinear modeling is based on a fiber discretization of an RC column section. Each fiber is modeled as either nonlinear concrete or steel spring, whose load-deformation characteristics are calculated from the section of fiber and material properties. The steel spring that models the reinforcing bars consists of three sub-springs, i.e., steel bar sub-spring, lap splice spring, and anchorage bond-slip spring connected in series from top to bottom. By combining the steel stress versus slip of the lap splice, the stress-deformation of steel bar and the steel stress-slip of bars anchored into the footing, the nonlinear steel spring model is derived. The analytical responses are found to be close to experimental ones. The analysis without lap splice springs included may result in an erroneous overestimation in the strength and ductility of columns.

Key Words
Tri-uniform bond stress model; nonlinear modeling; fiber-reinforced polymer; fiber discretization; lap splice spring.

Address
Amorn Pimanmas: Sirindhorn International Institute of Technology, Thammasat University, Pathum Thani 12121, Thailand
Dam Xuan Thai: Civil Engineering Department, The National University of Civil Engineering, Hanoi, Vietnam


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