Pre-selected Target Drift Research Articles

Evaluation of ground motion scaling methods on drift demands of energy-based plastic designed steel frames under near-fault pulse-type earthquakes

In the present study, the effects of six different ground motion scaling methods on inelastic response of nonlinear steel moment frames (SMFs) are studied. The frames were designed using energy-based PBPD approach with the design concept using pre-selected target drift and yield mechanism as performance limit state. Two target spectrums are considered: maximum credible earthquake spectrum (MCE) and design response spectrum (DRS). In order to investigate the effects of ground motion scaling methods on the response of the structures, totally 3216 nonlinear models including three frames with 4, 8 and 16 stories are designed using PBPD approach and then they are subjected to ensembles of ground motions including 42 far-fault and 90 near-fault pulse-type records which were scaled using the six different scaling methods in accordance to the two aforementioned target spectrums. The distributions of maximum inter-story drift over the height of the structures are computed and compared. Finally, the efficiency and reliability of each ground motion scaling method to estimate the maximum nonlinear inter-story drift of special steel moment frames designed by energy-based PBPD approach are statistically investigated, and the most suitable scaling methods with the lowest dispersion for two groups of earthquake ground motions are introduced.

Performance-Based Plastic Design of Moment Frame-Steel Plate Shear Wall as a Dual System

Steel Plate Shear Wall (SPSW) is an emerging seismic load-resistant system that, compared to other systems, enjoys the advantages of stable ductile behavior, fewer detailing requirements, rapid constructability, and economy. American seismic provisions decree that a SPSW should be designed as a moment frame with a web infill plate. Specifically, in case of buildings taller than 160 ft, it decrees that a dual system must be used. This paper presents a method of Performance-Based Plastic Design (PBPD) to design steel moment frame-SPSW as a dual lateral load-resisting system. PBPD method uses pre-selected target drift and yield mechanism as its main criteria. For a specified hazard level, the design base shear is calculated based on energy work balance method, employing pre-selected target drift. Plastic design of dual frame system has been performed to meet the pre-selected yield mechanism. As presented in the paper, design procedure involves solving a system of five equations with five variables to determine the proportion of SPSW and moment frame shear, shear wall thickness, and beam/ column sections. It has been considered that a four-story structure is designed with the proposed method. Seismic performance of this dual frame system, designed with the proposed method, is evaluated by nonlinear static and dynamic analysis for both Design Basis Earthquake (DBE) and Maximum Credible Earthquake (MCE). Result analysis is in accord with the assumptions, satisfying all the performance objectives. PBPD is a direct design method in which no iteration is needed to achieve the performance objectives. Determining the proportion of SPSW and moment frame shear is an exclusive capability of this procedure.

Effect of Increasing Ductility Factors on the Performance of a Steel Moment Resisting Frame Designed by the Performance Based Plastic Design Method attuned with Indian Code of Practice

Effect of increasing ductility factors on the performance of a steel moment resisting frame has been studied. The frame has been designed for ductility factors 2,3,4,5 and 6 using the performance based plastic design method which is based on the “strong column–weak beam” principle. Pre-selected target drift and yield mechanism are chosen as performance criteria. The design base shear for selected hazard level is determined by equating the work needed to push the structure monotonically up to the target drift to the corresponding energy demand of an equivalent SDOF oscillator. Plastic design as per Indian Code of practice is performed to detail the frame members and connections in order to achieve the intended yield mechanism and behavior. It was observed that as the ductility factor increases, the lateral loads decrease and hence section becomes lighter leading to optimum strength utilization. No unexpected failure is observed in most of the frames and their performance under seismic loads satisfies the “strong column–weak beam” principle.

Evaluation of Response Reduction Factor of a Reinforced Cement Concrete Building Designed by Performance Based Plastic Design Method and Limit State Design Method

The Performance Based Plastic design method uses pre-selected target drift and yield mechanism as performance criteria due to which total collapse of structure can be prevented. A fifteen storey Reinforced Cement Concrete frame was designed using the displacement based Performance Based Plastic Design (PBPD) method and currently used force based Limit State Design (LSD) method. The comparative seismic performance evaluation of the frames was then carried out by assessing the Response Reduction factor as well as the failure pattern. Results show that PBPD frame is found to have a higher response reduction factor as compared to the LSD frame. Also total collapse of the frame is prevented in the PBPD frame as hinges are formed in beams only.

Performance-Based Plastic Design Method for Steel Concentrically Braced Frames Using Target Drift and Yield Mechanism

Under severe earthquakes, steel concentrically braced frames (SCBFs) will experience large inelastic deformations in an uncontrolled manner. According to the energy-work balance concept, a performance-based plastic design (PBPD) methodology for steel concentrically braced frames was presented here. This method uses pre-selected target drift and yield mechanism as key performance limit states. The designed base shear for selected hazard levels was derived based on work-energy balance equations. Plastic design was performed to design bracing members and connection nodes in order to achieve the expected yield mechanism and behavior. The method has been successively applied to design a six-storey steel concentrically braced frame. Results of inelastic dynamic analyses showed that the story drifts were well within the target values, thus to meet the desired performance requirements. The proposed method provided a basis for performance-based plastic design of steel concentrically braced frames.

Development of the Performance Based Plastic Design for Steel Concentric Braced Frames and Evaluation by Energy Methodology

This paper presents the development of performance based plastic design (PBPD) method to design steel concentric braced frames (SCBFs). The design base shear is obtained based on energy-work balance equation using preselected target drift and yield mechanism. Also, the energy-work balance can be applied to estimate seismic demands, herein called the energy spectrum method. PBPD method was originally developed to design SCBFs. The results were too conservative. For further improvement, this paper presents some modifications such as C2-Factor method and P-delta effect in energy-work balance equation to give a better estimate of design base shear. For validity, three baselines frames (3, 6, 9-story) are designed according to AISC 2005 seismic provisions (Baseline frames). Then, the frames are designed based on the Original PBPD method (Original PBPD method). Finally, they are designed based on modifications applied on PBPD method (Modified PBPD frames). These frames are subjected to extensive inelastic pushover and time-history analyses. The Results show that the Modified PBPD frames meet all the intended performance objectives in terms of yield mechanisms and target drifts whereas the Baseline frames show very poor response due to premature brace fractures leading to unacceptably large drifts and instability. Also, Modified PBPD frames show that the structures having 20%–25% weight less than the Original PBPD can meet the performance objectives. Moreover, the drift demands obtained from energy spectrum method significantly correspond with the results of time history analyses.

Performance-based plastic design method for steel concentric braced frames

This paper presents a performance-based plastic design (PBPD) methodology for the design of steel concentric braced frames. The design base shear is obtained based on energy–work balance equation using pre-selected target drift and yield mechanism. To achieve the intended yield mechanism and behavior, plastic design is applied to detail the frame members. For validity, three baseline frames (3, 6, 9-story) are designed according to AISC (Seismic Provisions for Structural Steel Buildings, American Institute of Steel Construction, Chicago, 2005) seismic provisions (baseline frames). Then, the frames are redesigned based on the PBPD method. These frames are subjected to extensive nonlinear dynamic time-history analyses. The results show that the PBPD frames meet all the intended performance objectives in terms of yield mechanisms and target drifts, whereas the baseline frames show very poor response due to premature brace fractures leading to unacceptably large drifts and instability.

The Effects of Yield Mechanism Selection on the Performance based Plastic Design of Steel Moment Frame

This study concentrates on the effect of selecting a desirable yield mechanism that has a significant effect on seismic design and response of structures designed by Performance Based Plastic Design (PBPD) method. In PBPD method, the design base shear is obtained on the basis of energy-work balance equation implementing pre-selected target drift and yield mechanism. With considering the importance of selection of yield mechanism, a parametric study has been done considering the different types of yield mechanisms to design a model of steel moment frame. The results obtained by nonlinear time history analyses shown that the complete sway mechanism (strong columns-weak beams) is the most efficient in terms of required design base shear for a given target story drift. It also should be noted that it is often impossible to estimate the column moment demand during the event of sever ground motions because they undergo large moments not only from those delivered from beams but also from their own deformation. Therefore, assuming only the criteria of strong column-weak beam mechanism in PBPD method can’t prevent the yielding in columns. In this paper to improvement of PBPD method, some solutions are represented to precisely obtain the required moment of columns to prevent their yielding. Because the yielding of columns leads to form undesirable mechanisms before the structure reaches the pre-selected target drift. For example, a 10 story frame has been designed based on PBPD method using strong column-weak beam mechanism. The frame has been redesigned considering all represented equations of this study (modified PBPD frame). The results obtained by nonlinear static and dynamic analyses show that the modified PBPD frame perform according to expectations in terms of yield mechanism and target drift levels whereas the PBPD frame suffer large story drifts due to flexural yielding of the columns.

Development of the performance based plastic design for steel moment resistant frame

This paper presents the development of performance based plastic design (PBPD) method for steel moment frames with considering the gravity loads and P-Δ effects. In this method the design lateral forces are obtained from energy-work balance equation by using pre-selected target drift and yield mechanism. For further improvement of PBPD method, some solutions are represented to precisely obtain the required moment of columns in order to prevent their yielding that leads to form undesirable mechanisms in the structure. In order to show more validity of PBPD method, two model frames, 5 and 10story, are designed based on PBPD as well as elastic design method. The mentioned frames are evaluated by extensive nonlinear static pushover analysis and dynamic analysis. The results show that the frames designed by PBPD method reach the intended performance objectives in terms of yield mechanism and target drift levels. In contrast, the frame designed by Ed method experience large story drifts due to flexural yielding of the columns. Since PBPD method is a direct design method, little or no evaluation are needed after the initial design because the nonlinear behavior is built into the design process from the start.

Performance-Based Seismic Design of RC SMF Using Target Drift and Yield Mechanism as Performance Criteria

Reinforced concrete special moment frames (RC SMF) have been widely used as part of seismic force-resisting systems. Design methodologies and systematic procedures of RC SMF are needed which require no or little iteration after initial design in order to meet the targeted design objectives. This paper presents the first time application of the Performance-Based Plastic Design (PBPD) approach to RC SMF. The PBPD method uses pre-selected target drift and yield mechanisms as key performance objectives. These two design parameters are directly related to the degree and distribution of structural damage, respectively. Four baseline RC SMF (4, 8, 12 and 20-story) as used in the FEMA P695 were selected for this study. Those frames were redesigned by the PBPD approach. The baseline code designed frames and the PBPD frames were subjected to extensive inelastic pushover and time-history analyses. The seismic responses of the study frames met the targeted performance criteria with considerable improvement over the corresponding baseline code designed frames.

Performance-based plastic design method for buckling-restrained braced frames

This paper presents a performance-based plastic design (PBPD) methodology for the design of buckling-restrained braced frames (BRBFs). The design base shear is obtained based on energy–work balance using pre-selected target drift and yield mechanism. Three low-to-medium rise BRBFs (3-story, 6-story and 9-story) were designed by the proposed methodology and their seismic performance was evaluated through extensive nonlinear time-history analyses using forty ground motions representing the DBE and the MCE hazard levels. Both isotropic and kinematic hardening characteristics of buckling-restrained braces were considered in the modeling of their force–deformation behaviors. All BRBFs considered in this study reached the intended performance objectives in terms of yield mechanisms and target drift levels. Since PBPD is a direct design method, no iterations were carried out to achieve the performance objectives of BRBFs.

Performance-Based Plastic Design of Special Truss Moment Frames

This paper presents the results of a study in which a recently developed performance-based plastic design (PBPD) methodology was used to design the special truss moment frame (STMF) system rather than conventional elastic method. This newly developed performance-based method has been successfully applied to moment frames and also extended to eccentrically braced frames, buckling-restrained braced frames, and concentrically braced frames. The procedure begins by selecting a desired yield mechanism for the frame. Design base shear and lateral forces are determined from input spectral energy for a given hazard level needed to monotonically push the structure in the yielded state up to a pre-selected target drift. The frame members are then designed by following the plastic design method in order to develop the needed strength and the intended yield mechanism. A new seismic design lateral force distribution based on nonlinear dynamic behavior is also presented. The proposed design procedure was validated by extensive nonlinear dynamic analyses for a number of ground motion records. The results confirm the validity of the proposed method for the study STMFs in terms of meeting all the performance design objectives, such as target drifts and intended yield mechanism. An important advantage of the PBPD method is that, generally, no nonlinear analysis is needed to check the structural performance after the initial design.