Seismic Frames Research Articles

Stochastic Optimization of Dissipation Structures Based on Lyapunov Differential Equations and the Full Stress Design Method

This article presents a Lyapunov precise integral-based analysis method for seismic structures with added viscous fluid dampers. This study uses the full stress algorithm as the optimization method, considering the mean square of interstory drifts as the optimization objective, the position of the damper as the optimization object, and the random vibration analysis method as the calculation method to optimize seismic frame structures with viscous dampers. A precise integral solution is derived for the Lyapunov equation based on the general expression of the Lyapunov differential equation for the damping system under the excitation of a nonstationary stochastic process using two types of modulation functions: g(t)=1 and g(t)=t. Finally, the optimal damping arrangement is achieved using this method with a six-layer non-eccentric planar frame. In addition, the optimization results of this study are verified with those in the literature using time-history analysis, which verifies the feasibility and effectiveness of the proposed method. This study provides a method for the optimal configuration of dampers for seismic response of structures, which is beneficial for engineering applications and the protection of seismic structures.

Risk assessment of several hazards along railway network using AHP incorporated into GIS

Located in northeastern Algeria, the region of Constantinois is undoubtedly among the regions most affected by various risks related to rail networks. These phenomena are one of the major development issues and a major and permanent threat to the population and existing facilities. The risks associated with rail field transport are associated with several parameters such as soft geological formations, steep slopes, hydrographic network, seismic frame and mainly problems linked to human accident, suicide and stones thrown. In this context, the objective of this paper is the identification of risk-prone areas in the rail network linking Constantine to Skikda (Algeria). This in order to highlight the relations that exist between several parameters: geological conditions, local topography, flow hydrographic network, vegetation...etc., and hazard treat on railway network such as settlement or landslide risk anthropic risk (risk of stone thrown and suicide accident). The methodology used is based on a GIS approach to identify areas susceptible, it is based on the interpretation of satellite map, topographic, geological and other data. The GIS project developed will allow to superimpose and analyze the effect of several factors on railway network integrity, these factors and their respective weights are then calibrated with statistical tool by adopting the method "Analytical Hierarchy Process" AHP. The resulting susceptibility maps distinguishes several degrees of susceptibility of areas that may be affected by collapse or accident problems of rail platforms. The comparison with the inventory map of several accidents that have already been recorded by railways services shows that the results obtained from the spatial modeling are very satisfactory.

Optimum Design of Seismic Steel Frame Model Considering the Panel Zone and Viscous Dampers

Optimum Design of Seismic Steel Frame Model Considering the Panel Zone and Viscous Dampers

Influence of different seismic motion input modes on the performance of isolated structures with different seismic measures

AbstractIn order to obtain the influence of different seismic motion input modes on the performance of isolated structures with different seismic measures, the two aspects from near-fault seismic motion velocity pulse input and different dimension seismic motion input modes are studied. The finite element model of traditional seismic and base isolation frame structure with different aspect ratios is established. The actual near-seismic strong earthquake record with forward directional effect and slipping speed pulse is used as the input method of structural seismic motion to carry out nonlinear dynamics. The different dimensional seismic motion input method is selected as the quantitative, the tensile–compression stiffness ratio is the variable, and the time-history analysis of the isolation performance of a high-rise isolated structure is carried out. The experimental results show that for structures with an aspect ratio H/B of 1, 2, 3, and 4, the smaller the aspect ratio is, the better the damping effect is; the different dimensional vibration input has less isolation performance for the isolation bearing. From small to large, it is: one-dimensional vibration input, two-dimensional vibration input, three-dimensional vibration input.

Experimental study on typically designed double-sided plate-reinforced joints with middle columns

Beam-to-column joints in seismic moment frames would directly influence the behaviours of the connected members. When reinforced joint configurations were adopted to shift plastic hinges away from the field welds, columns in seismic steel frames would suffer larger inner forces and should be specially checked to control yielding mechanics. However, there were only few investigations on reinforced joints with typically-designed columns in multi-story frames, which limited the comprehensive evaluation of seismic beam-to-column joints especially for the reinforced joint configurations. In this investigation, the seismic behaviours of the cover-plate joint and the flange-plate joint, which are collectively referred to as plate-reinforced joints, were evaluated experimentally. Tests of four double-sided plate-reinforced joint specimens, taken from prototype seismic steel frames that were typically designed and checked by the Chinese code, were conducted under anti-symmetrical cyclic loads on the beam ends with axial forces in the columns. The test results were analysed to consider the seismic performances of the connections and members in the plate-reinforced joints, summarizing the characteristics of the failure modes, the resistance and the ductility. Specially, the seismic behaviour of the middle column with axial force, as well as the panel zone, was analysed. According to the test results, the flange-plate joints were more sensitive to the quality of the field complete-joint-penetration welds between the reinforcing plates and the column flanges than the cover-plate joints. The middle columns in typically-designed seismic frames by the Chinese code may not guarantee satisfactory seismic performances in the joint regions, and the panel zone that was designed based on the Chinese code might not allow the beam section to reach the plastic moment although it could effectively contribute to the joint deformability. Based on this study, practical recommendations for seismic design of connections and members in plate-reinforced joints were proposed.

Effect of Raft and Column Sizes on the Seismic Soil Structure Interaction Performance of Fifteen Storey Midrise Frame Structures

Seismic design of structures is usually executed by performing 1D free-field soil response analysis using design spectral acceleration charts given by codes. This method ignores soil structure interaction effects thus affecting structure-foundation-soil system behavior leading to imprecise design. Soil structure interaction refers to the dynamic behavior between the structure, underlying foundation and soil block. To understand the behavior of a 15 storey midrise concrete seismic frame structure rested on raft foundation and founded on silty sandy soil block, 3D nonlinear time history finite element simulations using Abaqus were performed. The effects of raft and column sizes were considered by modeling flexible and fixed based structures. All cases were hit at the bottom by El-Centro (1940) and Northridge (1994) earthquakes. The results were presented in terms of storey lateral deflection, inter-storey drift, shear force, foundation rocking and response spectrum. The results showed that the combination between the structure-foundation-soil natural frequencies along with the soil type used dictate the behavior of the midrise structure as well as SSI effects under the different raft and column sizes used. Therefore, a detailed study considering all above parameters must be performed by engineers to ensure safe and cost-effective designs.

Numerical model for investigating seismic performance of Prestressed Hollow Concrete (PHC) piles with Fiber section element

In the medium to high seismic zone, prestressed hollow concrete (PHC) pile for structural foundation should be designed with elastic behavior due to low ductility and dissipated energy. However, some Indonesian practical engineer has chosen PHC pile for pile-supported slab viaduct (PSSV) with medium seismic moment-resisting frame concept in a high-risk earthquake zone. Therefore, some nonlinear numerical simulations of PSSV structure in medium to high seismic zone need to be conducted to investigate its seismic performance. In the initial stage, a numerical model for investigating the seismic performance of PHC pile under flexural test was conducted. By implementing an appropriate plastic hinge length of forced beam-column with hinge elements, the flexural behavior of PHC piles to be simulated under both monotonic and cyclic loading. The fiber section was adopted to accommodate non-linear behaviour of material in the PHC pile cross section. As the results, the skeleton curves, the sectional strain distributions, and the hysteresis curves have good agreement results compared with the experimental results. Furthermore, based on the equal damping ratio calculation of the hysteresis curve, the PHC pile only achieve low energy dissipation, though the ductility capacity around 3. Finally, this numerical model approach could be adopted in the non-linear simulation of PSSV structure under seismic load.

Influence of FE Modelling Approaches on Vulnerabilities of RC School Buildings and Proposal of a CFRP Retrofitting Intervention

Background: The vulnerability assessment of existing school buildings against earthquakes represents a priority concern for society. In recent years, several countries promote seismic rehabilitation projects of school buildings, including the allocation of funds to regions with high seismic hazard. Objective: This research aims to highlight some key role aspects related to difficulties encountered in the numerical modelling of RC structures hosting school activities. This work evaluates the seismic vulnerability of school buildings located in the municipality of Trecastelli (Marche, Central Italy) to quantify the effective influence of typical and specific seismic vulnerabilities detected on the global seismic behaviour of each building. The effectiveness of a possible Carbon Fibre Reinforced Polymer (CFRP) local strengthening intervention, for the case study, aimed to confine unconfined beam-column joints is also considered. Methods: Three different numerical models of a Reinforced Concrete (RC) school building are implemented with the lumped plasticity, the distributed plasticity (fibre) and the 3D Continuum Finite Element (FE) approaches. Nonlinear static (pushover) analyses are performed to assess the global seismic behaviour of the structure, and the limitations to represent the reality with different approaches. After the seismic vulnerability assessment of the case study, a CFRP retrofitting intervention is proposed to confine external beam-column joints. Results: The comparison of the numerical results of three models shows that the fibre model is the least suitable means to represent shear problems, while the lumped plasticity model is closer to reality than the previous one even if it does not take into account the concomitance of bending, shear and axial force and the interaction between them in the inelastic response. Of course, the 3D Continuum model is the most accurate representation to describe the complex and combined mechanisms developed in the joint panels. Nonlinear static (pushover) analyses carried out on unreinforced and reinforced structures of Continuum model demonstrate that the Fibre Reinforced Polymer (FRP) strengthening improves the displacement capacity of the structure. Conclusion: This study has highlighted the strengths and weaknesses of different modelling types. The meaningful information about mechanisms developed in joints given by the 3D Continuum FE model is useful to identify shortcomings of the design project and to conceive a retrofitting strengthening intervention. CFRP sheets externally bonded on beam-column joints may improve the seismic frame performances without a significant change of the structural stiffness, promoting a ductile failure mode with a higher displacement capacity than the unreinforced case.

Loss impact factors for lifetime seismic loss assessment of steel concentrically braced frames designed to EC8

ABSTRACTThis study employs multiple earthquake time-history response simulations, and the FEMA P-58 performance assessment methodology to evaluate the influence of key design parameters on the lifetime seismic repair costs incurred by case study concentrically braced frames (CBFs) designed to Eurocode 8. The parameters considered include structural mass, stiffness (natural period) and ductility (behaviour factor). A new factor termed the Loss Impact Factor (LIF), is used to quantify the influence of each of these parameters on lifetime costs. Under dissipative seismic design principles, bracing members in CBFs may behave inelastically under infrequent, high-intensity earthquakes. Larger values of the design behaviour factor, q, selected by the structural engineer result in higher ductility demands during these earthquakes, but also reduce the design seismic action, leading to smaller, lighter and more flexible structural members. Hence, variations in one parameter necessarily influence the others, as well as initial construction cost. The variation in expected lifetime seismic repair costs with respect to each of these parameters, which is less clear, is the subject of this paper. Costs are shown to reduce with increased structural mass, stiffness and initial cost, with the impact of the latter two parameters generally increasing with both seismic hazard and frame height.

Displacement-Based Seismic Assessment for Precast Concrete Frames with Non-Emulative Connections

ABSTRACT The paper develops a methodology for the seismic vulnerability assessment, Displacement-Based Assessment (DBA), of one-story and multi-story precast concrete frames with non-emulative connections. The method is based on the Direct Displacement-Based Design procedure initially developed by Priestley. The DBA is particularly suitable for the evaluation of the seismic response of flexible structures, as it considers displacements as the leading parameters to estimate the seismic vulnerability. The proposed procedure specifically accounts for the influence of beam–column connections, P-∆ effects, and second mode of vibration. The validation has been performed by means of nonlinear time history analyses.

Seismic Simulation of U.S. and Japanese Type Steel Moment-Resisting Frame Structures Using Practical FEM Macro Models

Building structures around the world have been designed using various framing methods. In Japan, the two-way moment-resisting frame structure, which is designed as a 3D seismic frame with beams connected to the columns, with moment connections in both directions, is traditionally constructed. In contrast, in the United States and many other countries in high seismic regions, the one-way moment-resisting frame structure, which is designed as separate seismic and gravity frame structure with only a few expensive moment connections in seismic frames, is typically constructed. Structures with these different framing systems are likely to exhibit different seismic response and collapse mechanism when subjected to large earthquake excitation. However, the simulation up to complete collapse has almost not been conducted and safety margin to complete collapse of these different framing systems has not been sufficiently understood. In this study, seismic simulation of U.S. and Japanese type three-story steel moment-resisting frame structures is conducted using general-purpose finite element analysis program. Practical macro models used for the simulation are based on beam and shell elements. It is found that composite effects of floor slab accelerate column yielding in both U.S. and Japanese type steel frame structures and drift concentration may occur at relatively small ground motion level and eventually result in complete collapse.

Buckling Restrained Brace Deformation Measuring Device

Buckling Restrained Braces (BRB’s) have become common in seismic frames in earthquake areas. If a BRB performs as desired the steel core may yield but it is not easy to know the degree of yielding, or how much of the BRB earthquake life has been used up. To determine whether such a brace should remain as is, or whether it needs to be replaced, an inexpensive and simple measuring device that reports the deformations undergone is required. This paper discusses a study undertaken to develop such a device. Firstly, a literature study was undertaken and candidate devices were selected. Using Subjective Quantitative Analysis (SQA) and specific performance objectives the most appropriate of these was chosen. This device was then constructed and tested in a controlled environment. This mechanical device performed well through various stimulated earthquake cycles and events, is cheap, simple to install, and small. It provides cumulative and maximum displacement estimations and will be beneficial to the industry in post-event decision making.

Seismic-Proof Buildings in Developing Countries

The use of “ductile seismic frames”, whose proper seismic behavior largely depend upon construction details and specific design rules, may do not always lead to effective seismic resistant structures, as dramatically denounced by the famous Chinese artist Ai Weiwei in his artwork Straight. The artwork (96 tons of undulating metal bars that were salvaged from schools destroyed by the 2008 Sichuan, China earthquake, where over 5,000 students were killed) is a clear denounce against the corruption yielding to shoddy construction methods. The issue of safe constructions against natural hazards appears even more important in developing countries where, in most cases, building structures are realized by non-expert workers, or even by simple “people from the street”, who does not have any technical knowledge on construction techniques and seismic engineering. In the present paper, a brief history from the first frame structures to the more efficient wall-based structures is provided within earthquake engineering perspectives. The superior structural properties of box-type wall structures with respect to conventional frame structures envisage a change of paradigm from actual “ductility-based” Earthquake Engineering (centered on frame structures) towards 100% safe buildings through a “strength-based” design exploiting the use of box-type wall based structures.

Performance evaluation of self-centring steel-braced frame

A modern self-centring braced frame equipped with post-tensioned cables and replaceable fuses is capable of rocking on its foundation during an earthquake. The aim of this paper is to evaluate the seismic performance of a controlled-rocking braced frame and compare its efficiency with a similar fixed-based braced frame. A non-linear time history analysis is conducted for a set of archetypes, varying in height, seismic design category, and seismic frame type. A sensitivity analysis is performed to examine the effects of modelling and ground motion parameters. Results indicate that the rocking system is capable of enhancing the performance of a conventional braced frame by features such as the controlled rocking mode, self-centring and concentrated damage to replaceable fuses.

Seismic Performance Assessment of Multitiered Steel Concentrically Braced Frames Designed in Accordance with the 2010 AISC Seismic Provisions

AbstractMultitiered steel concentrically braced frames (CBFs) are commonly used to provide lateral resistance for tall single-story commercial, performing arts, sports, and industrial buildings. The seismic response of these frames is studied in this paper. A set of seven special concentrically braced frames (SCBFs), ranging from 9 to 30 m tall with two to six tiers, located in a high seismic area was designed according to the 2010 AISC Seismic Provisions. Fundamental behavior of the two- and four-tiered frames was investigated using three-dimensional (3D) finite element models with shell elements, with particular focus on the buckling response of the columns. The seismic frame response and column stability were then studied more broadly for all frames using more computationally efficient 3D finite element models with fiber-based beam-column elements, which were validated against the shell element models. Multitiered CBFs designed according to current multistory CBF procedures are shown to develop drift c...

Seismic Performance of Base-Isolation Building Subjected to Near-Fault Ground Motion with Velocity Pulse

The seismic response of the base-isolated structure can be reduced significantly in the far-field region compared to the conventional seismic structure. However, near-fault ground motions with velocity pulse may cause the adverse influence on the seismic performance of the base-isolation building, which needs to be investigated deeply. In this paper 6 ground motions with velocity pulse are selected as the input, and the seismic response of a 9 layers conventional seismic RC frame building and comparative base-isolation building with lead-core rubber bearings are obtained by nonlinear time history analysis. The result indicates that base-isolation building with lead-core rubber bearings are of good aseismic performance under the near-fault ground motions with velocity pulse.

Prediction of Column Axial Force in X-braced Seismic Steel Frames Considering Brace Buckling

According to the capacity design concept underlying current steel seimsic provisions, the braces in concentrically braced frames should dissipate seismic energy through cyclic tension yielding and compression buckling. On the other hand, the beams and the columns in the braced bay should remain elastic for gravity load actions and additional column axial forces resulting from the brace buckling and yielding. However, due to the difficulty in accumulating the yielding and buckling-induced column forces from different stories, empirical and often conservative approaches have been used in design practice. Recently a totally different approach was proposed by Cho, Lee, and Kim (2011) for the prediction of column axial forces in inverted V-braced frames by explicitly considering brace buckling. The idea proposed in their study is extended to X-braced seismic frames which have structural member configurations and load transfer mechanism different from those of inverted V-braced frames. Especially, a more efficient rule is proposed in combining multi-mode effects on the column axial forces by using the modal-mass based weighting factor. The four methods proposed in this study are evaluated based on extensive inelastic dynamic analysis results.

Comparison of Stiffness Degradation of Special-Shaped Column and Rectangular Column Structure in Earthquake

In this paper, using the finite element software PERFORM3D to establish the finite element analysis model for isolation and seismic frame structure with special-shaped column and rectangular column frame structure, and the overall structure of the moderate and strong elastic and nonlinear earthquake time-history analysis to get the dynamic characteristics, from two aspects of the damping coefficient in horizontal direction and the energy dissipation, investigation structure in earthquake and rare earthquake of superstructure stiffness attenuation. It can be drawn only seismic resistance measures are taken, the special-shaped column structure under rare earthquake stiffness attenuation speed is greater than the rectangular column, if after using base isolation technology, although the special-shaped column stiffness attenuation rate is still greater than the rectangular column, but the two energy dissipation ability.

The Anti-Seismic Numerical Simulation for a Multi-Storey Frame with Bamboo Engineering Materials

Bamboo has many good features, is an ideal material for the construction industry. The numerical simulation of multi-layer seismic frame structure of bamboo by hand shows that, for re-bamboo wood columns, typical of the two failure modes for the transverse deformation is too large can not continue to load and top of the fibers in the lateral pressure exploded; bamboo column can be restored in the unloaded more than 80% of deformation, has excellent elastic recovery; bamboo can withstand the load beam is actually controlled by the stiffness, not strength.

The Anti-Seismic Numerical Simulation for a Multi-Storey Frame with Bamboo Engineering Materials

Bamboo has many good features, is an ideal material for the construction industry. The numerical simulation of multi-layer seismic frame structure of bamboo by hand shows that, for re-bamboo wood columns, typical of the two failure modes for the transverse deformation is too large can not continue to load and top of the fibers in the lateral pressure exploded; bamboo column can be restored in the unloaded more than 80% of deformation, has excellent elastic recovery; bamboo can withstand the load beam is actually controlled by the stiffness, not strength.