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CONTENTS
Volume 9, Number 3, March 2000
 

Abstract
Computational procedure within the framework of return mapping technique has been presented to integrate the constitutive behavior of a concrete model. Developed by Ohtani and Chen, this concrete model is based on multiple hardening concept, and is rate-independent and associative. Consistent tangent operator suitable for finite element analysis is derived to preserve the rate of convergence. Accuracy of the integration technique is verified and compared with available experimental data. Computational efficiency is demonstrated by comparing with results based on elasto-plastic tangent.

Key Words
concrete, multiple hardening, plasticity, return mapping, consistent tangent operation

Address
Lam SSE, Hong Kong Polytech Univ, Dept Civil & Struct Engn, Hung Hom, Hong Kong
Hong Kong Polytech Univ, Dept Civil & Struct Engn, Hung Hom, Hong Kong
No Jiaotong Univ, Dept Civil Engn, Beijing, Peoples R China

Abstract
The study of the optimal damping ratio of a tuned liquid-column damper (or TLCD) attached to a single-degree-of-freedom system is presented. The tuned liquid-column damper is composed of two vertical columns connected by a horizontal section in the bottom and partially filled with water. The ratio of the length of the horizontal section to the effective wetted length of a TLCD considered as another important parameter is also presented for investigation. A simple pendulum-like model test is conducted to simulate a long-period motion in order to prove the effectiveness of TLCD for vibrational control. Comparisons of the experimental and analytic results of the TLCD, TLD (tuned-liquid damper), and TMD (tuned-mass damper) are included for discussion.


Key Words
TLCD, optimal damping ratio, design parameter, experiment and comparison

Address
Chen YH, Natl Taiwan Univ, Dept Civil Engn, Taipei 10764, Taiwan
Natl Taiwan Univ, Dept Civil Engn, Taipei 10764, Taiwan
Natl Taiwan Univ, Dept Naval Architecture & Ocean Engn, Taipei 10764, Taiwan

Abstract
The major sources of energy dissipation in steel frames with partially restrained (PR) connections are evaluated. Available experimental results are used to verify the mathematical model used in this study. The verified model is then used to quantify the energy dissipation in PR connections due to hysteretic behavior, due to viscous damping and at plastic hinges if they are formed. Observations are made for two load conditions: a sinusoidal load applied at the top of the frame, and a sinusoidal ground acceleration applied at the base of the frame representing a seismic loading condition. This analytical study confirms the general behavior, observed during experimental investigations, that PR connections reduce the overall stiffness of frames, but add a major source of energy dissipation. As the connections become stiffer, the contribution of PR connections in dissipating energy becomes less significant. A connection with a T ratio (representing its stiffness) of at least 0.9 should not be considered as fully restrained as is commonly assumed, since the energy dissipation characteristics are different. The flexibility of PR connections alters the fundamental frequency of the frame. Depending on the situation, it may bring the frame closer to or further from the resonance condition. if the frame approaches the resonance condition, the effect of damping is expected to be very important. However, if the frame moves away from the resonance condition, the energy dissipation at the PR connections is expected to be significant with an increase in the deformation of the frame, particularly for low damping values. For low damping values, the dissipation of energy at plastic hinges is comparable to that due to viscous damping, and increases as the frame approaches failure. For the range of parameters considered in this study, the energy dissipations at the PR connections and at the plastic hinges are of the same order of magnitude. The study quantitatively confirms the general observations made in experimental investigations for steel frames with PR connections; however, proper consideration of the stiffness of PR connections and other dynamic properties is essential in predicting the dynamic behavior.


Key Words
energy dissipation, partially restrained connections, sinusoidal loading, viscous damping, hysteretic damping, inelastic analysis, MDOF elasto-plastic system, time history analysis, moment resisting steel frames, connection stiffness

Address
Reyes-Salazar A, Univ Autonoma Sinaloa, Fac Ingn, Culiacan, Sinaloa, Mexico
Univ Autonoma Sinaloa, Fac Ingn, Culiacan, Sinaloa, Mexico
Univ Arizona, Dept Civil Engn & Engn Mech, Tucson, AZ 85721 USA

Abstract
The seismic design recommendations of the Jordan Code for Loads and Forces (JC) are evaluated, based on comparisons with analytical studies and the Uniform Building Code. It was established that the overall safety ensured by the implementation of these recommendations is not consistent with the established seismic risk in Jordan and the intended objectives of the code. A new zoning map is proposed with effective peak ground acceleration values. The different period formulae of the code were studied and were found to grossly underestimate the fundamental period when compared with analytically derived values or other codes\' formulae. Other factors including the dynamic, soil, importance and behavior factors are discussed. It was determined that the JC\'s lateral load distribution formulae clearly lead to smaller internal forces than both dynamic analysis and UBC loads, even when those loads are normalized to give the same base shear. The main reason for this is attributed to the limited allowance for a backlash force in the JC.


Key Words
earthquake, seismic, code, lateral load

Address
Saffarini HS, Univ Jordan, Dept Struct Engn, Amman 11942, Jordan
Univ Jordan, Dept Struct Engn, Amman 11942, Jordan

Abstract
The governing differential equations for free vibration of multi-step orthotropic shear plates with variably distributed mass, stiffness and viscous damping are established. It is shown that a shear plate can be divided into two independent shear bars to determine the natural frequencies and mode shapes of the plate. The jk-th natural frequency of a shear plate is equal to the square root of the square sum of the j-th natural frequency of a shear bar and the k-th natural frequency of another shear bar. The jk-th mode shape of the shear plate is the product of the j-th mode shape of a shear bar and the k-th mode shape of another shear bat. The general solutions of the governing equations of the orthotropic shear plates with various boundary conditions are derived by selecting suitable expressions, such as power functions and exponential functions, for the distributions of stiffness and mass along the height of the plates. A numerical example demonstrates that the present methods are easy to implement and efficient. It is also shown through the numerical example that the selected expressions are suitable for describing the distributions of stiffness and mass of typical multi-storey buildings.

Key Words
vibration, plates, tall buildings, natural frequencies, mode shapes

Address
Li QS, City Univ Hong Kong, Dept Bldg & Construct, Struct Dynam Res Ctr, Tat Chee Ave, Kowloon, Hong Kong
City Univ Hong Kong, Dept Bldg & Construct, Struct Dynam Res Ctr, Kowloon, Hong Kong

Abstract
This study discusses on the experimental and analytical results of the global buckling tests, carried out on aluminum alloy double layer space grids composed of tubular members, ball joints and connecting bolts at the member ends, with the purpose of demonstrating the effectiveness of a simplified analysis method using an equivalent slenderness ratio for the members. Because very few experiments have been carried out on this type of aluminum space grids, the buckling behavior is investigated experimentally over the post buckling regions using several space grid specimen with various values for the member slenderness ratio. The observed behavior duping the experiments is compared with the analytically obtained results. The comparison is made based on two different schemes; one on the plastic hinge method considering a bending moment-axial force interaction for members and the other on a method using an equivalent slenderness ratio. It is confirmed that the equivalent slenderness method can be effectively applied, even in the post buckling regions, once the effects of the rotational rigidity at the ball joints are appropriately evaluated, because the rigidity controls the buckling behavior. The effectiveness of the equivalent slenderness method will be widely utilized for estimation of the ultimate strength, even in post buckling regions for large span aluminum space grids composed of an extreme large number of nodes and members.

Key Words
space grids, ball joints, aluminum, buckling behavior

Address
Hiyama Y, Sumitomo Light Met Ind Ltd, Ohta Ku, 4-1-23 Heiwajima, Tokyo 1430006, Japan
Sumitomo Light Met Ind Ltd, Ohta Ku, Tokyo 1430006, Japan
Fukui Univ, Dept Civil & Architectural Engn, Fukui 9108507, Japan
Toyohashi Univ Technol, Dept Civil & Architectural Engn, Toyohashi, Aichi 4418122, Japan

Abstract
This paper develops a simplified, but effective, algorithm in obtaining critical slab design moments for parking garages. Maintaining the uniformly distributed load concept generally adopted in the design of building structures, this paper also introduces the equivalent vehicle load factors, which can simulate the vehicle load effects without taking additional sophisticated numerical analyses. After choosing a standard design vehicle of 2.4 tons through the investigation of small to medium vehicles made in Korea, finite element analyses for concentrated wheel loads were conducted by referring to the influence surfaces. Based on the obtained member forces, we determined the equivalent vehicle load factors for slabs, which represent the ratios for forces under vehicle loads to these under uniformly distributed loads. In addition, the relationships between the equivalent vehicle load factors and sectional dimensions were also established by regression, and then used to obtain the proper design moments by vehicle loads. The member forces calculated by the proposed method are compared with the results of four different approaches mentioned in current design codes, with the objective to establish the relative efficiencies of the proposed method.

Key Words
parking garage, vehicle loads, distributed loads, equivalent vehicle load factors, slab

Address
Kwak HG, Korea Adv Inst Sci & Technol, Dept Civil Engn, Yusung Ku, 373-1 Kusung Tong, Taejon 305701, South Korea
Korea Adv Inst Sci & Technol, Dept Civil Engn, Yusung Ku, Taejon 305701, South Korea


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