Yield Base Shear Research Articles

Seismic design method based on limit state for prefabricated RCS frames

The prefabricated reinforced concrete column-steel beam (RCS) frame is an innovative and efficient structural system. To promote the application of the prefabricated RCS frame, a practical seismic design method based on the limit state design was proposed. The elastic method based on the bearing capacity of components was adopted to design frames with different ground motion intensities. When the designed frames are under the strong-column-weak-beam criterion, the capacity and demand values of over-strength factors were calculated, and the over-strength factors were adopted to calculate the yield base shear. Based on the yield base shear and yield mechanism, the semi-rigid connections were designed according to the plastic method, while the beams and columns were designed based on the capacity method. The proposed design method was successfully applied to a six-story prefabricated RCS frame and validated by inelastic analyses. Furthermore, the proposed method can also provide references for other prefabricated frames.

Design of lead-rubber-bearing isolation systems using a grasshopper optimisation algorithm

Seismic isolation is an efficient method for improving the seismic behaviour of building structures. Sensitivity analysis of the behaviour of base-isolated structures is essential for investigating the effects of various mechanical and environmental factors on the performance of seismic isolation systems. In this study, the optimal design of a lead-rubber-bearing seismic isolation system was investigated by considering irregular mass conditions and near-fault seismic excitation. The grasshopper optimisation algorithm was used to optimise the design of the isolation system. Sensitivity analysis of the seismic response of the isolated structures was carried out for the mechanical parameters of the isolation system, mass irregularity in the building and near-fault earthquakes. The results proved the efficiency of the algorithm in optimal design problems for structural isolation systems. Also, the sensitivity analysis of the seismic behaviour of base-isolated structures showed that the yield base shear index had the most important effects in analysis. Furthermore, mass irregularity showed a negligible influence on the behaviour of the isolated structures.

Application of a Novel Optimization Algorithm in Design of Lead Rubber Bearing Isolation Systems for Seismic Rehabilitation of Building Structures

Various mechanical and geometrical parameters have different effects on the isolation system's performance. Thus, a sensitivity study of the isolated structures' behavior is an essential matter. In this regard, the isolation systems should be designed using optimization approaches to consider the effects of the different factors. In this study, the optimal design of the lead rubber bearing (LRB) seismic isolation was conducted by considering mass irregularity and near-fault seismic excitation effects. Also, sensitivity analysis of the behavior of the considered isolated buildings was implemented concerning the mechanical parameters of the LRB system. A nonlinear time history dynamic analysis was used here, and the design optimization of the LRB isolator was programmed using the newly introduced grasshopper optimization algorithm (GOA). The main purpose was to investigate the ability of the GOA to optimize the design parameters of the LRB-isolated frames. The results proved the desirable ability of the GOA to solve optimal design problems for isolation systems. Also, the sensitivity analysis of the seismic behavior of LRB base-isolated structures showed that the yield base shear index had the most important effects. Also, the mass irregularity parameter showed a negligible influence.

Derivation of yield force coefficient for RC frames considering energy balance and P-delta effects

Currently, prominent energy balance concept can efficiently be used to calculate the yield base shear force of structures. Energy balance equation is an additional constraint for the balance of seismic input energy by the energy absorption of the structure. This equation can be defined as the sum of elastic and plastic energies of structural systems using elastic and plastic load-deformation characteristics and the total energy dissipation capacity can finally be equated to the seismic energy demand. The objective of this paper is to present a procedure for the determination of energy-based yield force coefficient of reinforced concrete (RC) frame structures considering P-delta effects. The total of elastic and plastic energies are computed by means of elastic spectral velocity and energy modification factor, which is originally derived for structural systems with geometric nonlinearity. Total inelastic energy of single-degree-of-freedom (SDOF) system is transformed into the total inelastic energy of the multi-degree-of-freedom (MDOF) system using the conversion based on structural dynamics. Plastic energy of MDOF system is formulated after total seismic energy demand is obtained. It is accordingly equated to the total work done by inelastic MDOF structure with P-delta effects and consequently, a dimensionless yield force coefficient is derived. Nonlinear static analyses are performed for selected multi-story RC frames and yield force coefficients are compared with the results of the energy-based formulation. The results show that the proposed formulation taking P-delta effects into account can be effectively used to estimate the yield force coefficient of RC frame structures.

Comparative Analysis of Structural Damage Potentials Observed in the 9.12 Gyeongju and 11.15 Pohang Earthquakes

In this paper, comparative analysis of the 9.12 Gyeongju and 11.15 Pohang earthquakes was conducted in order to provide probable explanations and reasons for the damage observed in the 11.15 Pohang earthquake from both earthquake and structural engineering perspectives. The damage potentials like Arias intensity, effective peak ground acceleration, etc observed in the 11.15 Pohang earthquake were generally weaker than those of the 9.12 Gyeongju earthquake. However, in contrast to the high-frequency dominant nature of the 9.12 Gyeongju earthquake records, the spectral power of PHA2 record observed in the soft soil site was highly concentrated around 2Hz. The base shear around 2 Hz frequency was as high as 40% building weight. This frequency band is very close to the fundamental frequency of the piloti-type buildings severely damaged in the northern part of Pohang. Unfortunately, in addition to inherent vertical irregularity, most of the damaged piloti-type buildings had plan irregularity as well and were non-seismic. All these contributed to the fatal damage. Inelastic dynamic analysis indicated that PHA2 record demands system ductility capacity of 3.5 for a structure with a fundamental period of 0.5 sec and yield base shear strength of 10% building weight. The system ductility level of 3.5 seems very difficult to be achievable in non-seismic brittle piloti-type buildings. The soil profile of the PHA2 site was inversely estimated based on deconvolution technique and trial-error procedure with utilizing available records measured at several rock sites during the 11.15 Pohang earthquake. The soil profile estimated was very typical of soil class D, implying significant soil amplification in the 11.15 Pohang earthquake. The 11.15 Pohang earthquake gave us the expensive lesson that near-collapse damage to irregular and brittle buildings is highly possible when soil is soft and epicenter is close, although the earthquake magnitude is just minor to moderate (M 5+).

STRUCTURAL CHARACTERISTICS OF TRADITIONAL THATCHED HOUSES IN OLD POST TOWNS

We report the progress of our research on seismic performance estimation of a traditional thatched house in Ouchi-Juku, Fukushima prefecture, registered as an IPDGHB in 1981, based on field surveys. First, we carried out a field survey of two existing thatched houses to understand their structural properties and conducted microtremor measurements of these houses and examined their ground to analyze their vibrational characteristics. Based on vibration mode of the house, it was found that the amplitude was large on the front side, which was used as often as a souvenir shop and Japanese restaurant, because the front of the house had less walls. Finally, we calculated the yield base shear coefficient as an indicator of seismic performance and compared it with the regression functions of traditional town houses in Kyoto. It is found that the thatched house in Ouchi-Juku had a higher shear force than a wooden house in Kyoto.

Effect of masonry infill walls with openings on nonlinear response of reinforced concrete frames

Masonry infill walls are unavoidable parts of any building to create a separation between internal space and external environment. In general, there are some prevalent openings in the infill wall due to functional needs, architectural considerations or aesthetic concerns. In current design practice, the strength and stiffness contribution of infill walls is not considered. However, the presence of infill walls may decisively influence the seismic response of structures subjected to earthquake loads and cause a different behavior from that predicted for a bare frame. Furthermore, partial openings in the masonry infill wall are significant parameter affecting the seismic behavior of infilled frames thereby decreasing the lateral stiffness and strength. The possible effects of openings in the infill wall on seismic behavior of RC frames is analytically studied by means of pushover analysis of several bare, partially and fully infilled frames having different bay and story numbers. The stiffness loss due to partial opening is introduced by the stiffness reduction factors which are developed from finite element analysis of frames considering frame-infill interaction. Pushover curves of frames are plotted and the maximum base shear forces, the yield displacement, the yield base shear force coefficient, the displacement demand, interstory drift ratios and the distribution of story shear forces are determined. The comparison of parameters both in terms of seismic demand and capacity indicates that partial openings decisively influences the nonlinear behavior of RC frames and cause a different behavior from that predicted for a bare frame or fully infilled frame.

宮崎県の重要伝統的建造物群保存地区（日向市美々津）の伝統木造住宅構造調査

Mimitsu in Miyazaki prefecture is selected to grasp the seismic performance of traditional wooden houses. Seismic performance of 8 houses is evaluated based on microtremor measurements and structural investigation. As results, there are 2 types of traditional houses. One is the type with rooms in a line, and the other is with rooms in 2 lines. The traditional houses have skip floor structure, and the vibration mode is complicated. Yield base shear coefficients of houses with rooms in 2 lines are lower than those of houses with rooms in a line.

Determination of lateral strength and ductility characteristics of existing mid-rise RC buildings in Turkey

This paper presents a comprehensive work on determination of yield base shear coefficient and displacement ductility factor of three to eight story actual reinforced concrete buildings, instead of using generic frames. The building data is provided by a walkdown survey in different locations of the pilot areas. Very detailed three dimensional models of the selected buildings are generated by using the data provided in architectural and reinforcement projects. Capacity curves of the buildings are obtained from nonlinear static pushover analyses and each capacity curve is approximated with a bilinear curve. Characteristic points of capacity curve, the yield base shear capacity, the yield displacement and the ultimate displacement capacity, are determined. The calculated values of the yield base shear coefficients and the displacement ductility factors for directions into consideration are compared by those expected values given in different versions of Turkish Seismic Design Code. Although having sufficient lateral strength capacities, the deformation capacities of these typical mid-rise reinforced concrete buildings are found to be considerably low.

Response modification factor of suspended zipper braced frames

The suspended zipper bracing system is suggested to reduce the flaws of ordinary zipper braced and concentric inverted <i>V</i> braced frames. In the design procedure of suspended zipper bracing systems, columns and top story truss elements are strengthened. This bracing system show different performances and characteristics compared with inverted <i>V</i> braced and ordinary zipper frames. As a result, a different response modification factor for suspend zipper frames is needed. In this research paper, the response modification factor of suspended zipper frames was obtained using the incremental dynamic analysis. Suspended zipper braced frames with different stories and bay lengths were selected to be representations of the design space. To analyze the frames, a number of models were constructed and calibrated using experimental data. These archetype models were subjected to 44 earthquake records of the FEMA-P695 project data set. The incremental dynamic analysis and elastic dynamic analysis were carried out to determine the yield base shear value and elastic base shear value of archetype models using the OpenSEES software. The seismic response modification factor for each frame was calculated separately and the values of 9.5 and 13.6 were recommended for ultimate limit state and allowable stress design methods, respectively.

Impact of column-to-beam strength ratio on the seismic response of steel MRFs

The strong-column/weak-beam seismic design concept in moment resisting frames is perhaps one of the least well-understood design provisions. This study is aimed at improving the understanding of the effect of column-to-beam strength ratio (CBSR) on several seismic performance measures. Through nonlinear analyses of 3-, 9-, and 20-story moment resisting frame, the impacts of CBSR on member ductility demands, maximum inter-story drifts, and floor acceleration amplifications are investigated. For each frame, the value of CBSR is varied by changing the yield strength of the material and/or by altering sizes of the columns. The probabilities of exceeding certain performance limits are investigated through fragility analyses. The single curvature bending of the columns within a story is found to be inevitable due to the participation of higher modes of vibration. Consequently, under large ground motions, the yielding of the columns is expected even for CBSRs larger than 2.0. The fragility relationships were used to calculate the design force modification factors needed for achieving a comparable probability of column yielding for different values of CBSR. The values of the yield base shear and the inter-story drifts were found to depend more on the strength of the beams than the value of CBSR. The floor acceleration amplification was found to be the least sensitive demand parameter to the CBSR.

Lateral load resistance of bridge piers under flexure and shear using factorial analysis

Tie spacing, concrete and steel properties, amount of reinforcement and column height are factors (or parameters) that can affect the performance of bridge piers under lateral loads. These parameters differ significantly from older bridges to modern bridges. Here, a detailed parametric study has been performed to understand the effects of these factors and their interactions on limit states of bridge columns using factorial analysis. Fiber modeling approach has been implemented to determine the performance of bridge piers (such as cracking base shear, cracking displacement, yield base shear, yield displacement, crushing base shear/shear capacity, displacement at crushing/shear failure and ductility) under lateral loads. This study shows that simple predictive equations can be derived from the parametric study, to estimate the cracking, crushing and yielding displacement of a bridge pier with reasonable accuracy.

単層ラチスドームの地震時の損傷評価方法に関する基礎的研究

The present paper proposes a simple and efficient procedure to evaluate seismic fragility and risk of spatial structures and studies on seismic loss of a dome structure. As an example for calculating the seismic risk, a numerical investigation is performed for a single layer lattice dome supported by a substructure implemented with ductile braces as buckling restrained braces. The analysis of seismic loss is based on a simple rule for judging the damage to both of the structural and non-structural elements. The effectiveness and feasibility of the study is discussed and necessity of some kind of energy absorbing devices is suggested for more damage reduction through several examples with different yield base shear coefficient.

EVALUATION OF SEISMIC CAPACITY OF SPORT HALLS BASED ON ELASTO-PLASTIC EARTHQUAKE RESPONSE ANALYSIS

The present paper discusses on a seismic performance of braces of sport halls reinforced by hysteretic dampers installed in the longitudinal direction. Based on the elasto-plastic dynamic analysis depending on varying input levels, the ductility index, d F, and the seismic performance index, d Is , are re-studied. As numerical parameters, a capacity limit deformation and a yield base shear coefficient of original braces are considered together with the natural period of original substructure and the yield base shear coefficient of added hysteretic dampers, and their effects on the ductility index are investigated. The ductility index of the reinforced structure can be estimated by the strength ratio of hysteretic dampers to those of original braces, and the seismic performance index of the reinforced structure, d IsR, can be estimated based on that of the original structure, d Is0.

STRUCTURAL FIELD SURVEY AND SEISMIC PERFORMANCE EVALUATION FOR WOODEN HOUSES OF KYOTO-KITAYAMA TYPE IN MIYAMA

This paper reports the results of evaluation on seismic performance for wooden houses of Kyoto-Kitayama Type in Miyama based on field survey and static loading test for mock test frames. Major findings from the research are as follows: (1) In the field survey, structural and vibration characteristics are clarified. (2) In the experiment, it is find out that structural factors founded on the specification of Miyama have different strength from the past restoring models: such as wooden wall, Sashigamoi and so on. (3) Applying the restoring model conducted the experiment results, the maximum change of yield base shear coefficient is 40%.

ESTIMATION OF DYNAMIC DUCTILITY INDEX OF BRACES IN LONGITUDINAL DIRECTION OF SPORT HALLS BASED ON ENERGY BALANCE RESPONSE

The present paper discusses on a dynamic seismic performance index of structure, d Is, and a dynamic ductility index, d F, of a brace installed in the longitudinal direction of sport halls. Based on the result of the elasto-plasitc dynamic analysis depending on various input levels, d F and d Is are re-studied. As numerical parameters, a yield base shear coefficient of braces of substructure, Cy , and a capacity limit deformation of braces as well as hysteresis types are considered, and their effects on d F and d Is are investigated. Furthermore, the method of estimation for d F is proposed using an absorbed energy principle, and the validity of the proposal method is proven by comparing the responses of the dynamic response analysis with those based on the proposed method.

STUDY ON EVALUATION OF DYNAMIC DUCTILITY INDEX OF SPORT HALLS BASED ON ELASTO-PLASTIC EARTHQUAKE RESPONSE ANALYSIS

The present paper discuses on a dynamic seismic performance index of structure, d Is, and a dynamic ductility index, d F, of a brace installed in the longitudinal direction of school sport halls. Based on the result of the elasto-plasitc dynamic analysis depending on various input levels, d F and d Is are re-studied. As numerical parameters, a yield base shear coefficient of braces of substructure, Cy , and a capacity limit deformation of braces as well as hysteresis types are considered, and their effects on d F and d Is are investigated.

LEVEL OF SEISMIC PROTECTION IN DIFFERENT EDITTIONS OF THE EGYPTIAN CODE OF LOADS

The last edition of the Egyptian Code of Loads (ECOL) was released by the end of year 2008. The seismic provisions in this edition are almost completely different compared with those in the 1993 edition while some specific changes are presented relative to the 2003 edition. The major significant changes in the seismic provisions revealed in the different editions are reviewed. The effect of the variation in these provisions between the different editions of the ECOL on the level of seismic protection presented by the code calculated base shear is analyzed and discussed. The analyzed provisions include seismic zones and mapping, period equations, soil site conditions, building importance factor, and ductility level. These provisions are applied to two types of structures which are moment resisting frames (MRF) and dual system consists of shear wall-moment resisting frames (SW-MRF). The considered height of buildings covers almost all code permitted range of heights. It is found that the provisions in the 1993 edition yield base shear much less than the values obtained using 2008 edition especially for low to medium height buildings located in medium and high seismic zones.

IMPACT OF SEISMIC PROVISIONS IN DIFFERENT EDITIONS OF THE EGYPTIAN CODE OF LOADS

The last edition of the Egyptian Code of Loads (ECOL) was released by the end of year 2008. The seismic provisions in this edition are almost completely different compared with those in the 1993 edition while some specific changes are presented relative to the 2003 edition. The major significant changes in the seismic provisions revealed in the different editions are reviewed. The impact of these provisions on the level of seismic protection for different types of structures with different heights is analyzed and discussed. An analytical analysis is carried out to compare and verify the applicability of these methods and the protection level they introduce. The modal response spectrum (MRS) analysis is carried out using the elastic design spectrum specified by the 2008 ECOL while the time history analysis (THA) is applied using seven different real earthquake excitations selected to match the specified elastic spectrum and soil type. Suggestion to rationally enhance the seismic protection level obtained from the multiple response spectrum is presented and emphasized. This study extends to analyze and compare our seismic provisions with those appeared in different international codes for sites with similar conditions. It is found that the provisions in the 1993 edition yield base shear much less than the values obtained using 2008 edition especially for low to medium height buildings located in medium and high seismic zones. Also, it is found that some provisions in the new edition need to be urgently reconsidered.

Capacity Related Properties of RC Frame Buildings in Turkey

The capacity curves of various structural systems that are used in the HAZUS methodology to determine seismic vulnerability were developed based on the seismic design codes. These capacity curves are, therefore, very idealistic and do not take into account variations in the regional design practice. This article presents the results of nonlinear static analyses of representative reinforced concrete frame buildings located in Turkey to obtain their capacity curves. A representative set of buildings was selected from existing RC buildings. The parameters such as yield over-strength ratio, fundamental period, post elastic stiffness, yield and ultimate drift ratios, and yield base shear coefficient have been obtained from the idealized capacity curves. These parameters are used in HAZUS to determine seismic response of buildings under a given hazard level. This seismic response is then used in predetermined fragility curves to estimate the expected loss for the particular building type. The capacity curves developed herein for Turkish buildings were compared with other studies and HAZUS recommendations.