Severe Earthquake Ground Motions Research Articles

Cyclic behavior of channel-encased braces incorporating round HSS

Bracings made with cold-formed round hollow structural shapes (HSS) are commonly utilized in ductile concentrically braced frames (CBFs) in seismic regions for their efficiency in terms of high load-bearing capacity and ease of construction. Bracings are expected to sustain a ductility demand that ranges between 10 and 20 without fracture when ductile CBFs subject to severe earthquake ground motions. However, the experimental findings accentuate that ductile braces, even those with round HSS that possess impractically small diameter-to-wall thickness ratios (D/t), are prone to premature fracture. Thus, developing a simple and cost-effective performance-enhancing system for existing conventional CBFs incorporating round HSS could be imperative to mitigate the potential seismic risk. For this purpose, an existing round HSS is encased in two channels to form a buckling-controlling mechanism that is expected to improve the seismic hysteretic behavior, consequently, the energy dissipation capacity of ductile braces. Experimental and parametric numerical studies have been conducted to comprehend the level of improvement in the cyclic behavior and the impact of geometric parameters (i.e., slenderness and D/t ratios). The overarching results indicate that channel-encased bracing improves the seismic hysteretic behavior, yielding a stable and symmetric cyclic response. In addition, the results suggest that the optimal design parameters, including gap amplitude and encasing thickness, play a critical role in achieving desired ductility level.

Structural Behavior of steel frame Infilled with Ferrocement Precast Panel S ubjected to Lateral Load

Background: When a severe earthquake ground motion hits the structure even if it doesn’t collapse it may undergoes inelastic deformations. Steel structure infilled with precast panels becomes less efficient when subjected to large lateral loads like strong wind and earthquake. Hence assessment of actual performance of steel frames provided with infills in the event of earthquake is essential. Methods: In the current study, a prototype model of steel frame size 4m x4m bay & 4m height with G+2 story is scaled down and subjected to lateral seismic load by conducting shake table test to assess modal frequencies, the same structure is modelled in Hypermesh and analyzed in Nastran, ETABS software. The results obtained are validated for a 16X16m bay of 4m height commercial complex of G+9 Multi-storeyed structure infilled with Ferrocement Precast panels analysed in ETABS software for base shear, response spectrum and pushover analysis to assess the performance of the structure. Findings: The frequency from modal analysis was found to be 45.21 Hz, for G+2 storied model in ETABS, values obtained for frequency, base shear, performance point of the structure are in appreciable. Novelty: As per the traditional earthquake design methods, structures are designed for less forces than maximum considered for earthquake. The overall performance of the structure is found to be safe even infilled with Ferrocement precast panels. Advantages: Ferrocement panels as infills has benefit as they are slender from structural point of view. Compared with steel bare frame dynamic behavior of bare steel frame which is infilled with Ferrocement precast panel subjected to lateral loads is high that helps in assessing the damage in the event of an earthquake in critical zone V. Keywords: Infill; Ferrocement precast panels; Pushover Analysis; Performance point; Response spectrum

Development of a double-stage yielding damper with vertical shear links

This study proposes a novel hybrid damper called vertical links system with double-stage yielding (VLDY). The VLDY damper consists of two replaceable vertical shear links connected in series, located within a moment-resisting frame (MRF). When the MRF sustains lateral deformation, the minor link yields in shear. The inelastic shear rotation of the minor link increases till the engagement of the lockout mechanism. Thereafter, the inelastic deformation occurs in the major shear link, and the entire system enters the second yielding stage. The minor link can be adjusted to dissipate the input energy in relatively small inter-story drift levels during moderate earthquakes, and the major link maintains the structural integrity under severe earthquake ground motions. A validated nonlinear finite element modeling protocol in ABAQUS/standard was utilized to examine the applicability and cyclic response of the proposed system. The results showed that the VLDY device could provide stable energy dissipation capacity in a wide range of inter-story drift levels ranging from 0.3% to 4%. In addition, the cyclic secant stiffness, energy dissipation capacity, and equivalent viscous damping ratio of the VLDY-equipped frames significantly increased compared with those of the bare frames. Based on the results, a minimum free span-to-depth ratio of 7 has been suggested to ensure the prevention of the steep moment gradient on the story beams.

An investigation of P-delta effect in conventional seismic design and direct displacement-based design using elasto-plastic SDOF systems

The seismic responses of structures are always influenced by P-Δ effects. The significance of this effect may be negligible when the structure responds elastically but is very important when the structure responds into inelastic range. The P-Δ effect usually increases the displacement response of structures. It may even cause dynamic instability when the structure subjected to severe earthquake ground motions. In conventional seismic design codes, the P-Δ effect usually leads to an increase in design base shear. The same approach is used in direct displacement-based design. Various researchers have proposed different relationships for base shear increase which can be used in different seismic design approaches such as force-based design and performance-based design. In this paper, the proposed expressions are reviewed extensively and their adequacy is evaluated by detail. Then two main purposes are pursued: (1) the development of new expressions for strength amplification factor due to P-Δ effect for current force-based design seismic codes; and (2) the modification of equivalent viscous damping or the required additional base shear considering the P-Δ effect in direct displacement-based design procedure. For this purpose, a new algorithm based upon elasto-plastic SDOF system analyses is presented. The algorithm is implemented 102,500 times overall for different periods, ductility levels, stability indices and different earthquake ground motions that each implementation needs a large amount of trial and error process in linear and nonlinear SDOF systems. The results seem to present a good development of the P-Δ effect relations for the seismic design procedures.

Seismic behavior of special truss moment frame with double hollow structural sections as chord members

Research work carried out on steel special truss moment frames (STMFs) with double-angle sections as chord members during the 1990s led to the formulation of design code provisions. Further research results using double-channel specimens resulted in a modified equation for the expected vertical shear strength of the central special segments, Vne, and has been incorporated into the current AISC Seismic Provisions for Structural Steel Buildings. Double hollow structural sections (double-HSS) have the advantages of minimizing lateral torsional buckling and maximizing compactness in the flanges as compared to single HSS with the same flexural capacity. In this research, double-HSS members were proposed for the chord and web members of STMFs instead of double-angle, double-channel, or single-HSS. Double-HSS can effectively delay flange local buckling and enhance rotational ductility due to reduced width-to-thickness ratio (b/t) without increasing the wall thickness of the members. A full-scale STMF subassemblage with double-HSS as truss members was tested under large displacement reversals to simulate a severe earthquake ground motion. Testing results indicate that using double-HSS truss members is a viable alternative for STMFs in high seismic regions. Plastic hinge models are also suggested for computer analysis and design of non-yielding members outside of the special segments.

A Simple Evaluation Method of Seismic Resistance of Residential House under Two Consecutive Severe Ground Motions with Intensity 7

In the 2016 Kumamoto earthquake in Japan, two severe ground shakings with the seismic intensity 7 (the highest level in Japan Metheorological Agency (JMA) scale; approximately X-XII in Mercalli scale) occurred consecutively on April 14 and April 16. In the seismic regulations of most countries, it is usually prescribed that such severe earthquake ground motion occurs once in the working period of buildings. In this paper, a simple evaluation method is presented on the seismic resistance of residential houses under two consecutive severe ground motions with intensity 7. Therefore the proposed method can be used for the design of buildings under two consecutive severe ground motions. The present paper adopts an impulse as a representative of near-fault ground motion and two separated impulses are used as the repetition of intensive ground shakings with the seismic intensity 7. Two scenarios to building collapse (collapse limit in terms of zero restoring force with P-delta effect and collapse limit in terms of maximum deformation) under two repeated severe ground shakings are provided and energy consideration is devised for the response evaluation. The validity and accuracy of the proposed theories are discussed through numerical analysis using recorded ground motions.

外付け式層間変形制御装置による中低層建築物の地震応答制御

This study proposes a seismic response control device which prevents mid- and low-rise buildings from collapsing at specific story under severe earthquake ground motions. The device consists of the frame and the passive damper, which are mounted outside of the building. First, we constructed an analytical model of the device using a mass-spring-damper system and then performed time history seismic response analysis of the four-story steel buildings. We confirmed that the proposed device equalizes deflection of all the stories and reduces the maximum story deflection without excessive increase of the maximum response acceleration.

Seismic response and damage development analyses of an RC structural wall building using macro-element

Numerical simulation of the non-linear behavior of (RC) structural walls subjected to severe earthquake ground motions requires a reliable modeling approach that includes important material characteristics and behavioral response features. The objective of this paper is to optimize a simplified method for the assessment of the seismic response and damage development analyses of an RC structural wall building using macro-element model. The first stage of this study investigates effectiveness and ability of the macro-element model in predicting the flexural nonlinear response of the specimen based on previous experimental test results conducted in UCLA. The sensitivity of the predicted wall responses to changes in model parameters is also assessed. The macro-element model is next used to examine the dynamic behavior of the structural wall building-all the way from elastic behavior to global instability, by applying an approximate Incremental Dynamic Analysis (IDA), based on Uncoupled Modal Response History Analysis (UMRHA), setting up nonlinear single degree of freedom systems. Finally, the identification of the global stiffness decrease as a function of a damage variable is carried out by means of this simplified methodology. Responses are compared at various locations on the structural wall by conducting static and dynamic pushover analyses for accurate estimation of seismic performance of the structure using macro-element model. Results obtained with the numerical model for rectangular wall cross sections compare favorably with experimental responses for flexural capacity, stiffness, and deformability. Overall, the model is qualified for safety assessment and design of earthquake resistant structures with structural walls.

Seismic response of a continuous bridge with bearing protection devices

Unseating of bridges during earthquakes results from the failure of bearings and insufficient seat length. In case of elastomeric bearings, large deformations of the superstructure occur, under severe earthquake ground motions and additional protection measures are necessary. The combination of a displacement restraining device with the elastomeric bearing can prevent bearing failure. This paper evaluates the performance of four different types of protection devices to limit the displacement of the superstructure during earthquakes: (1) rigid stopper device, (2) yielding stopper device, (3) steel restrainer, and (4) superelastic shape memory alloy (SMA) restrainer. Analytical models for all the protection devices have been developed and seismic response of an existing bridge with elastomeric bearings and different protection devices has been evaluated for five strong ground motion records scaled in the frequency domain. The results show that all the protection devices have comparable performance in preventing the failure of bearing during an earthquake.

A PROPOSAL ON PERFORMANCE EVALUATING GUIDE TO PROMOTE SEISMIC REINFORCEMENT OF TRADITIONAL HOUSES

Existing traditional houses have high risk of collapse during severe earthquake ground motion and the results of the seismic diagnosis are far below the required values in the Building Standard Low. However, renovation for earthquake-resistant structures is not carried out smoothly.It is one of the causes of that owners cannot imagine the relationship between seismic reinforcement and its effect. This paper described a performance evaluating guide to promote seismic reinforcement of traditional houses.

Performance of Reinforced Concrete Columns Designed for Flexure under Severe Displacement Cycles

This paper investigates the effect of displacement history on the deformation response of concrete columns controlled by flexure. Twelve full-scale column specimens designed for pure flexure failure were tested. Two typical column designs, representing substandard and code-conforming columns, were used in the tests. The main variable in the experiments was the imposed displacement history. Results showed that the deformation-based performance limits proposed for substandard columns by Eurocode 8 and ASCE/SEI 41 are very conservative, which may lead to misleading results in the seismic risk assessment of existing substandard concrete structures. Eurocode 8 performance limits predicted the experimental performance of code-conforming columns well, but ASCE/SEI 41 performance limits appeared conservative in predicting the experimental performance of column plastic hinges designed to fail in flexure under moderate axial load levels. Analytical studies on single degree of freedom structures representing flexural column behavior revealed that the effect of displacement history on the target drift demands of concrete structures is significant under severe earthquake ground motions. These findings can be used to improve the displacement-based criteria developed for modeling and seismic performance assessment of columns.

A Modified Equation for Expected Maximum Shear Strength of the Special Segment for Design of Special Truss Moment Frames

Special truss moment frame (STMF) is a relatively new type of steel structural system that was developed for resisting forces and deformations induced by severe earthquake ground motions. The system dissipates earthquake energy through ductile special segments located near the mid-span of the truss girders. The other elements outside the special segments, such as truss members, girder-to-column connections, and columns, are designed based on the expected vertical shear strength (Vne) of the special segment and are expected to remain elastic during a major earthquake. As a consequence, overestimation of in the special segment can result in significant over-design of the elements outside the special segment. This study shows that the equation for expected shear strength in the current AISC Seismic Provisions can be quite conservative, thereby leading to considerable over-design of members outside the special segment. Based on more realistic assumptions, a modified expression for is proposed in this paper, which results in a better estimation of the expected shear strength while maintaining an adequate safety margin. The proposed expression was validated by using previous experimental results as well as nonlinear static and dynamic analyses (to determine the seismic demand in the special segment). A design equation of for STMF using multiple Vierendeel panels in the special segment is also proposed.

On-Line Learning Failure-Tolerant Neural-Aided Controller for Earthquake Excited Structures

This paper presents an on-line learning failure-tolerant neural controller capable of controlling buildings subjected to severe earthquake ground motions. In the proposed scheme the neural controller aids a conventional H controller designed to reduce the response of buildings under earthquake excitations. The conventional H controller is designed to reduce the structural responses for a suite of severe earthquake excitations using specially designed frequency domain weighting filters. The neural controller uses a sequential learning radial basis function neural network architecture called extended minimal resource allocating network. The parameters of the neural network are adapted on-line with no off-line training. The performance of the proposed neural-aided controller is illustrated using simulation studies for a two degree of freedom structure equipped with one actuator on each floor. Results are presented for the cases of no failure and failure of the actuator on each of the two floors under several earthquake excitations. The study indicates that the performance of the proposed neural-aided controller is superior to that of the H controller under no actuator failure conditions. In the presence of actuator failures, the performance of the primary H controller degrades considerably, since actuator failures have not been considered for the design. Under these circumstances, the neural-aided controller is capable of controlling the acceleration and displace- ment structural responses. In many cases, using the neural-aided controller, the response magnitudes under failure conditions are com- parable to the performance of the H controller under no-failure conditions.

NUMERICAL STUDY OF COLLAPSE BEHAVIOR OF STEEL BUILDINGS DUE TO EXTREMELY HIGH SEISMIC LOAD

This paper focuses on the methodology for modeling the dynamic behavior of steel structures due to severe earthquake ground motions. The development of the Improved Applied Element Method for analyzing the entire behavior of large-scale steel structures up to total failure is briefly discussed. The main features of the method are illustrated. The presented case-studies show different collapse mechanisms of moment-resistance steel frame structure under severe ground motions. The results show high capability on simulating the observed damage of many steel structures due to recent earthquakes.

Behavior of Timber Pile-to-Cap Connections under Cyclic Lateral Loading

The pile-to-cap connection is a critical region in the structure that may experience inelastic behavior during severe earthquake ground motions. Although timber piles are extensively used in construction, little research has been devoted to studying the behavior of timber pile-to-cap connections under cyclic lateral loading, or to develop an improved understanding of the seismic design requirements of these connections. This paper presents an experimental investigation to assess the strength capability of timber pile-to-cap connections. The experimental study was conducted on full-scale timber specimens with different embedment lengths of the pile into the concrete beam. On the basis of the experiments, a theory to predict the lateral capacity of such connections was developed. The study highlighted the significance of wood compression perpendicular to the grain, wood hardness, and embedment length of pile into cap in evaluating the performance of such connections under lateral loads.

Energy Balance Assessment of Base-Isolated Structures

This paper explores the use of energy concepts in the analysis of base-isolated structures subject to severe earthquake ground motions. We formulate the energy balance equations in moving- and fixed-base coordinate frames and provide new physical insight into the time-dependent behavior of individual terms. Conventional wisdom in earthquake engineering circles is that systems with base isolation devices should be economically competitive and designed to: (1) minimize input energy, and (2) maximize the percentage of input energy dissipated by damping and inelastic mechanisms. Through the nonlinear time-history analysis of a base-isolated mass-spring system subject to an ensemble of severe ground motion inputs, we demonstrate that improvements in objective (2) often need to be balanced against increases in input energy. Hence, by itself, objective (1) presents an overly simplified view of desirable behavior.

崩壊メカニズムが異なる建物の構造特性係数の極値について

Observation of the damage induced by earthquakes indicates that buildings suffered severer damage in certain specific parts and collapsed in one story. This damage concentration is not preferable from the view point of seismic safety of buildings. Therefore, the weak-beam-strong-column concept is introduced to seismic design in order to avoid single story collapse. This design concept is due to the design basis relying on the ductility of the structure in case of severe earthquake ground motions. Therefore many seismic codes in the world adopt a structural characteristic factor that is to reduce seismic design forces considering an energy absorbing capacity of a structure. This paper discusses the extreme of the structural characteristic factor for different types of collapse mechanism.

A direct displacement‐based seismic design procedure to fulfill multiple performance objectives

Damage evidence after the Chi‐Chi earthquake highlighted the im‐portance of performance‐based earthquake engineering (PBEE), which stresses the inelastic behavior of structural systems under severe earthquake ground motions. In this paper, a direct displacement‐based seismic design procedure is implemented and demonstrated through an example to fulfill multiple performance objectives in practical design.

Approximate Evaluation of Deflection Amplification Factor

In seismic design provisions, the maximum story drift occurring in major earthquakes is estimated by amplifying the drifts computed from an elastic analysis at the prescribed design seismic force level with a deflection amplification factor. A survey of several seismic design provisions indicates that the deflection amplification factor, in most of the provisions, is independent of significant factors such as ductility ratio, fundamental period, and number of stories. In this paper, a statistical evaluation of deflection amplification factor is presented in order to indicate the parameters that have an effect on this factor. Elastoplastic multidegree of freedom (MDOF) models with various dynamic characteristics are first considered. Consequently, nonlinear and corresponding linear time history analyses for 21 severe earthquake ground motions are performed in order to obtain structural response data, which are then used to derive an empirical formula for the deflection amplification factor. Finally, an app...

X型制振プレース付剛節架構の機構と弾塑性性状について : (その1)引張接合型プレース架構

In the previous papers, we presented a new effective hysteretic damper and showed it had good restoring force characteristics and enough energy absorption capacity for a severe earthquake ground motion. In this paper, a tension connected braced frame with the hysteretic damper is proposed. The various kinds of loading tests and F.E.M. analyses of one story - one bay scaled frames with the hysteretic damper are performed for verifying the mechanism of the present frame and clarifying the required sectional properties of the brace member. It shows that the tension connected braced frame with the hysteretic damper has a good mechanism, which prevent compressive axial force in the brace, and therefore the brace buckling is not occurred even if the brace has relatively large slenderness ratio. So that the repeated, large drift of the frame causes no hysteresis loop deterioration of the damper.