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CONTENTS
Volume 40, Number 3, November10 2011
 

Abstract
As bridge conditions in the United States continue to deteriorate, rapid bridge replacement procedures are needed. Decked precast prestressed concrete (DPPC) girders are used for rapid bridge construction because the bridge deck is precast with the girders eliminating the need for a cast-in-place slab. One of the concerns with using DPPC girders as a bridge construction option is the durability of the longitudinal joints between girders. The objectives of this paper were to propose a method to use a spring element modeling procedure for representing welded steel connector assemblies between adjacent girders in DPPC girder bridges, perform a preliminary study of bridge performance under multiple loading scenarios and bridge configurations, and discuss model flexibility for accommodating future field data for model verification. The spring elements have potential to represent the contribution of joint grout materials by altering the spring stiffness.

Key Words
bridges; concrete; finite element model; spring elements; welded shear connectors

Address
Matthew Z. Smith, Yue Li and William M. Bulleit: Department of Civil and Environmental Engineering, Michigan Technological University, 1400 Townsend Dr., Houghton, MI 49931-1295, USA

Abstract
Seismic isolated building structures are examined in this study. The triple concave friction pendulum (TCFP) is used as a seismic isolation system which is easy to be manufactured and enduring more than traditional seismic isolation systems. In the TCFP, take advantage of weight which pendulum carrying and it\'s geometry in order to obtain desirable result of seismic isolation systems. These systems offer advantage to buildings which subject to severe earthquake. This is result of damping force of earthquake by means of their internal constructions, which consists of multiple surfaces. As the combinations of surfaces upon which sliding is occurring change, the stiffness and effective friction change accordingly. Additionally, the mentioned the TCFP is modeled as of a series arrangement of the three single concave friction pendulum (SCFP) bearings. A two dimensional- and eight- story of a building with and without isolation system are used in the time history analysis in order to investigate of the effectiveness of the seismic isolation systems on the buildings. Results are compared with each other to emphasize efficiency of the TCFP as a seismic isolation device against the other friction type isolation system like single and double concave surfaces. The values of the acceleration, floor displacement and isolator displacement obtained from the results by using different types of the isolation bearings are compared each other. As a result, the findings show that the TCFP bearings are more effective devices for isolation of the buildings against severe earthquakes.

Key Words
seismic isolation; single concave friction pendulum; double concave friction pendulum; triple concave friction pendulum; severe earthquake

Address
Muhammet Yurdakul: Department of Civil Engineering, Bayburt University, Bayburt, Turkey
Sevket Ates: Department of Civil Engineering, Karadeniz Technical University, Trabzon, Turkey

Abstract
This paper deals with the bifurcations of non-semi-simple eigenvalues at critical point of Hopf bifurcation to understand the dynamic behavior of the system. By using the Puiseux expansion, the expression of the bifurcation of non-semi-simple eigenvalues and the corresponding topological structure in the parameter space are obtained. The zero-order approximate solutions in the vicinity of the critical points at which the multiple Hopf bifurcation may occur are developed. A numerical example, the flutter problem of an airfoil in simplified model, is given to illustrate the application of the proposed method.

Key Words
eigenvalue bifurcations; non-semi-simple eigenvalues; Hopf bifurcation; zero-order approximation solution; nonlinear systems

Address
Yu Dong Chen, Chun Yan Pei and Su Huan Chen: College of Mechanical Science and Engineering, Nanling Campus, Jilin University, ChangChun 130025, P.R. China

Abstract
This paper focuses on post-buckling analysis of Timoshenko beams with various boundary conditions subjected to a non-uniform thermal loading by using the total Lagrangian Timoshenko beam element approximation. Six types of support conditions for the beams are considered. The considered highly non-linear problem is solved by using incremental displacement-based finite element method in conjunction with Newton-Raphson iteration method. As far as the authors know, there is no study on the post-buckling analysis of Timoshenko beams under uniform and non-uniform thermal loading considering full geometric non-linearity investigated by using finite element method. The convergence studies are made and the obtained results are compared with the published results. In the study, the relationships between deflections, end rotational angles, end constraint forces, thermal buckling configuration, stress distributions through the thickness of the beams and temperature rising are illustrated in detail in postbuckling case.

Key Words
geometrical non-linearity; post-buckling analysis; total lagrangian finite element model; Timoshenko beam; non-uniform temperature rise

Address
Turgut Kocaturk and Seref Doguscan Akbas: Department of Civil Engineering, Yildiz Technical University, Davutpasa Campus, 34210 Esenler- stanbul, Turkey

Abstract
Periodic and quasi-periodic Timoshenko beams on Pasternak foundation are investigated using the differential quadrature method. Not only band gaps in the beams but also the dynamic response of them is analyzed. Numerical results show that vibration in periodic beams can be dramatically attenuated when the exciting frequency falls into band gaps. Different from the band structures of periodic beams without foundation, the so-called critical frequency was found because of the Pasternak foundation. Its physical meaning was explained in detail and a useful formula was given to calculate the critical frequency. Additionally, a comprehensive parameter study is conducted to highlight the influence of foundation modulus on the band gaps.

Key Words
vibration attenuation; periodic beams; band gap; dynamic response; Pasternak foundation

Address
Hong-Jun Xiang and Zhi-Fei Shi: School of Civil Engineering, Beijing Jiaotong University, Beijing 100044, China

Abstract
The eight-node 3D solid element is one of the most extensively used elements in computational mechanics. This is due to its simple shape and easy of discretization. However, due to the parasitic shear locking, it should not be used to simulate the behaviour of structural members in bending dominant conditions. Previous researches have indicated that the introduction of incompatible mode into the displacement field of the solid element could significantly reduce the shear locking phenomenon. In this study, an incompatible mode eight-node solid element, which considers both geometric and material nonlinearities, is developed for modelling of structural members at elevated temperatures. An algorithm is developed to extend the state determination procedure at ambient temperature to elevated temperatures overcoming initially converged stress locking when the external load is kept constant. Numerical studies show that this incompatible element is superior in terms of convergence, mesh insensitivity and reducing shear locking. It is also showed that the solid element model developed in this paper can be used to model structural behaviour at both ambient and elevated temperatures.

Key Words
incompatible mode; solid 3D element; shear locking; elevated temperature; initially converged stress locking

Address
Xinmeng Yu, Xiaoxiong Zha: Department of Civil and Environmental Engineering, Shenzhen Graduate School of Harbin Institute of Technology, Shenzhen 518055, China
Zhaohui Huang: Department of Civil and Structural Engineering, University of Sheffield, Sheffield S1 3JD, UK

Abstract
In the past decades, recycling use of demolished concrete was almost limited to the types of recycled coarse aggregate with a size of about 5-40 mm and recycled fine aggregate with a size of about 0-5 mm for concrete structures, and reuse of demolished concrete lumps (DCLs) with a size much larger than that of recycled aggregate, e.g., 50-300 mm, has been limited to roadbed, backfilling materials, or discarded to landfills. Treatment processes of DCLs are much simpler than those of recycled aggregate, leading to less cost and more energy-saving. In the future, the amount of demolished concrete is estimated to be much higher, so reuse of DCLs for concrete structures will become necessary. The objectives of this paper are to document the process of making reinforced concrete beams with DCLs, and to discuss the flexural and shear behaviors of those reinforced DCL beams through an experimental program, which includes three beams filled with DCLs and one conventional beam for investigating the flexural strengths and deformations, and 12 beams filled with DCLs and two conventional beams for investigating the shear strengths and deformations. The authors hope that the proposed concept offers another sustainable solution to the concrete industry.

Key Words
demolished concrete; reinforced concrete; beams; sustainability; flexural behavior; shear strength

Address
Bo Wu: State Key Laboratory of Subtropical Building Science, Department of Civil Engineering, South China Univ. of Technology, Guangzhou 510640, China
Zhe Xu: State Key Laboratory of Subtropical Building Science, Department of Civil Engineering, South China Univ. of Technology, Guangzhou 510640, China; Shenzhen General Institute of Architectural Design and Research, Shenzhen 518031, China
Zhongguo John Ma: Department of Civil and Environmental Engineering, University of Tennessee Knoxville, 223 Perkins Hall, Knoxville, TN 37996-2010, USA
Qiongxiang Liu: Shenzhen General Institute of Architectural Design and Research, Shenzhen 518031, China
Wei Liu: State Key Laboratory of Subtropical Building Science, Department of Civil Engineering, South China Univ. of Technology, Guangzhou 510640, China; Shenzhen General Institute of Architectural Design and Research, Shenzhen 518031, China

Abstract
Time delay inevitably exists in active control systems, and it may cause the degradation of control efficiency or instability of the systems. So time delay needs to be compensated in control design in order to eliminate its negative effect on control efficiency. Today time delay in linear systems has been more studied and some treating methods had been worked out. However, there are few treating methods for time delay in nonlinear systems. In this paper, an active controller for a nonlinear and hysteretic building structure with time delay is studied. The nonlinear and hysteretic behavior of the system is illustrated by the Bouc-Wen model. By specific transformation and augmentation of state parameters, the motion equation of the system with explicit time delay is transformed into the standard state space representation without any explicit time delay. Then the fourth-order Runge-Kutta method and instantaneous optimal control method are applied to the controller design with time delay. Finally, numerical simulations and comparisons of an eight-story building using the proposed time-delay controller are carried out. Simulation results indicate that the control performance will deteriorate if time delay is not taken into account in the control design. The simulations also prove the proposed time delay controller in this paper can not only effectively compensate time delay to get better control effectiveness, but also work well with both small and large time delay problems.

Key Words
nonlinear and hysteretic building structure; active control; time delay

Address
Kun Liu, Long-Xiang Chen and Guo-Ping Cai: Department of Engineering Mechanics, State Key Laboratory of Ocean Engineering, Shanghai Jiaotong University, Shanghai 200240, P.R. China


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