Jay Shen

Hysteresis model of bolted-angle connections

Abstract This paper presents a hysteretic model of bolted-angle connections for seismic analysis of semi-rigid steel frames with bolted connections. A semi-rigid beam-to-column connection is divided into a finite number of fiber elements. Hysteretic behavior of the fiber elements under repeated tension and compression has been established using the combined experimental and analytical results. The model has been implemented into a general purpose computer program and agrees well with experimental results. The main features of the model include: (1) Parameters of the model are directly related to a connection design; (2) Hysteresis rules are developed directly from comprehensive experiments specifically designed for modeling.

Hysteretic behavior of bolted-angle connections

Abstract This paper presents an experimental investigation on the hysteretic behavior of bolted-angle beam-to-column connections. The investigation focused on: (1) the inelastic behavior under large cyclic deformation, (2) the failure modes under cyclic loading, and (3) the energy-dissipation capacity of the bolted-angle connections. Two deformation patterns, distinguished by the relative strength of angles and bolts, had a significant influence on the hysteretic behavior of the connections. Based on the experimental results, hysteresis rules were established to lay a foundation for the development of a behavioral hysteresis model of bolted-angle connections.

Seismic vulnerability mitigation of liquefied gas tanks using concave sliding bearings

The aim of this paper is to evaluate the effectiveness of a concave sliding bearing system for the seismic protection of liquefied gas storage tanks through a seismic fragility analysis. An emblematic case study of elevated steel storage tanks, which collapsed during the 1999 İzmit earthquake at Habas Pharmaceutics plant in Turkey, is studied. Firstly, a fragility analysis is conducted for the examined tank based on a lumped-mass stick model, where the nonlinear shear behaviour of support columns is taken into account by using a phenomenological model. Fragility curves in terms of an efficient intensity measure for different failure modes of structural components demonstrate the inevitable collapse of the tank mainly due to insufficient shear strength of the support columns. A seismic isolation system based on concave sliding bearings, which has been demonstrated a superior solution to seismically protect elevated tanks, is then designed and introduced into the numerical model, accounting for its non-linear behaviour. Finally, a vulnerability analysis for the isolated tank is performed, which proves a high effectiveness of the isolation system in reducing the probability of failure within an expected range of earthquake intensity levels.

Estimation of seismic-induced demands on column splices with a neural network model

The current seismic design specification (AISC 341-05) requires that column splices in moment frames, when not made using complete joint penetration (CJP) welds, be designed to develop the flexural strength of the smaller connected column and the shear demand associated with flexural hinging at the top and bottom of a spliced column at a given story. AISC 341-05 assumes that the beam-to-column connection would reach its critical limit state before the column splice does. Estimating seismic demands on column splices involves both ground motion and structural parameters, i.e., it is a high order nonlinear and complex problem. This study presents a Neural Network (NN) model to estimate the seismic demands on column splices in low-, medium-, and high-rise steel moment frames. Nine input parameters and 6 output parameters were used to construct the NN model. The effect of each input parameter on the output parameters (seismic demands on column splices and frame) was investigated through a sensitivity analysis based on the NN model.

Seismic Evaluation of Existing Wharf Structures Subjected to Earthquake Excitation: Case Study

The ability of aging shore structures to resist design seismic forces located in high-seismicity regions has been a subject of interest for many researchers. Seismic design codes have become more stringent and suggest the use of new design methods, such as performance-based design. According to the Turkish Code for Shore Structures (TCSS 2008), a pile-wharf structure is expected to withstand a D1 level of ground motion (corresponding to a return period of 72 years) with minor or no damage and a D2 level of ground motion (corresponding to a return period of 475 years) with short-term loss of serviceability. In this study, nonlinear static analyses of the seismic performance of two existing pile-wharf structures were performed (pushover analyses) according to TCSS (2008). The results are presented here.

Seismic Energy Demands of Inverted V-Braced Frames

It is known that structures act a nonlinear movement when strong ground motion cycle begins. Energy concept has been progressive tool to evaluate the structural system associated with performance-based design. Energy-based design can be expressed as the balance of energy input and the energy dissipation capacity of the structure. Researches that have been usually done for single degree of freedom system are needed for multi degree of freedom systems (MDOFs) in framework of the energy-based design methodology. In this paper, energy parameters in term of total energy input and hysteretic energy are evaluated and observed changes in height of the buildings for the energy concept. Structures are selected to demonstrate low and medium-rise steel inverted V-braced frames examined in linear and nonlinear dynamic time history analysis. The results are developed to obtain seismic energy demands.

Designs of Special Concentrically Braced Frame Using AISC 341-05 and AISC 341-10

AbstractSpecial concentrically braced frames (SCBFs) are among the most common steel structures for resisting earthquake loads in high seismic regions. Concentrically braced frames (CBFs) are elastically designed as one vertical truss system to resist lateral loads through axial brace members when they are introduced. The explicit capacity-design approach has been fully incorporated into the newest seismic provisions for structural steel buildings. One new analysis section is added into AISC 341-10 to address the inelastic responses of SCBFs. Two separate structural analyses and one additional analysis are required for SCBFs in AISC 341-10. These analysis requirements significantly increase design efforts in typical design offices, and a comprehensive study to demonstrate how such an explicit inelastic design procedure would (or would not) significantly improve seismic performance of SCBFs appears to be justified. This paper summarizes the seismic design of three SCBFs with different heights, namely, 4, 1...

Seismic Energy Demands in Steel Moment Frames

This study presents an energy approach to the seismic evaluation of steel moment resisting frames. A structure subjected to strong ground motion is supposed that it shows nonlinear behavior. Energy parameters is a way to specify the structural damage. Input energy is depend on the characteristics of the structure and ground motion. Structural design can be defined as the equilibration of the input energy and the energy dissipation capacity of the structure. Structures subjected to eartquake are supposed to dissipate all the input energy. Studies based on energy concepts are usually applied to single-degree-of-freedom (SDOF) system. For multi-degree-of-freedom (MDOF), more researches and new simpler methodologies are still needed in performance based evaluation including energy parameters. In this study , low – medium and high rise steel moment frames and will be studied in linear and nonlinear time history analysis. The results obtained from these analysis are reviewed for seismic energy demands.

Amplified Seismic Loads in Steel Moment Frames

This study focuses on exploring the seismic axial loads for columns in steel moment resisting frames (SMRFs) under strong ground motions. For this purpose, the increases in axial loads are investigated at the maximum lateral load level and the corresponding lateral displacement. The results are presented in terms of maximum amplification factors (Ω0) of all frame columns under the selected ground motions and axial load-moment levels in columns. four typical steel moment resisting frames representing typical low, medium and high rise steel buildings are designed based on the seismic design requirement in ASCE 7-10 and AISC 341-10 . An ensemble of ground motions range from moderate to severe are selected to identify the seismic response of each frames. Two sets of ground motions corresponding to 10% and 2% probability of exceedance are used in nonlinear dynamic time history analyses.