Direct Displacement-based Design Approach Research Articles

Application of Endurance Time Method in Seismic Assessment of RC Frames Designed by Direct Displacement-Based Procedure

This paper addresses the Direct Displacement-Based Design (DDBD) approach of multi-story RC frame structures consistent with changes ‎to design criteria between Turkish earthquake codes of TSC-2007 and TBEC-2018. The corresponding response modification factor (R) of structures designed based on the DDBD approach is also estimated in this research. The design base shear forces of both codes are compared considering different R factors and also with that of the DDBD approach. The results showed that the DDBD approach, as per TBEC-2018, provides RC frame structures with higher R values compared to the similar approach in accordance with TSC-2007. The Endurance Time (ET) method is a time history-based procedure for seismic assessment of ‎structures ‎under intensifying dynamic excitations aided to judge their performance at various intensity levels. Since, up to now, the ET method has not been considered to evaluate the performance of the structures designed by the DDBD approach, this paper addresses this issue. The ET ‎performance curves of RC frames show that structures designed by the DDBD approach in ‎accordance with TBEC-2018 exhibit higher Interstory Drift Ratios (IDRs) values than TSC-2007 at various hazard levels.

SEISMIC VULNERABILITY ASSESSMENT OF BASE-ISOLATED RC FRAME BUILDING USING DDBD METHOD

The direct displacement-based design (DDBD) method is widely used worldwide because it allows structures to be designed based on their expected performance criteria. The DDBD approach is utilized so that base-isolated building structures can meet the seismic performance parameters established by the displacement threshold. In the present study, an 8-story, 10-story and 12-storey base-isolated RC frame building is designed using the latest Indian seismic standards, with lead rubber bearing (LRB) as the base-isolation system. Force-based and DDBD methodology is implemented and compared for the selected base-isolated RC frame buildings. The nonlinear time-history analysis is conducted to evaluate the nonlinear lateral response of the RC frame buildings. The results indicated that the traditional force-based method shows almost 12% less top-storey displacement than the DDBD approach. The DDBD approach provides enhanced reliability, simplicity, and convenience in seismic design for base-isolated building frames with LRBs, making the observations more dependable and easier to employ.

Impact of ground motion directionality (RotDnn) on the coupled and uncoupled inelastic response of RC circular cantilever columns

Directionality in the representation of earthquake demand for structural seismic design has surfaced as a subject of debate in recent years. Design spectra, as defined in building and bridge codes, account for directionality by considering the peak response in all possible orientations of the motion using the RotDnn measure, where “nn” is the percentile of the peak response. Current seismic hazard maps are based on ground motion models that use the RotD50 spectra (median peak response). However, since 2009, building codes have adopted RotD100 spectra (maximum peak response), raising concern among researchers and engineers. The first objective of this study is to evaluate the impact of design spectra definition, RotD50 or RotD100, on the bidirectional inelastic response of azimuth-independent RC systems. Upcoming updates to seismic hazard maps highlight the need of understanding the implication of this choice in bridge design. While previous research focused on the relationship between RotD50 and RotD100, this work assesses the impact of each definition on the inelastic seismic response of RC circular columns designed following the Direct Displacement-Based Design approach and verified through nonlinear time history analyses (NTHA) using ground motions from shallow crustal active and subduction zone regions. The ratios of NTHA to design displacement confirm that RotD100 spectra should be used to design azimuth-independent RC systems and provide the first known verification of DDBD for bidirectional loading (second objective). These ratios are a function of ductility level, tectonic regime, effective period, and coupling (which is the third objective). Overall results show that RC circular cantilever columns designed to RotD100 spectra show less deviation from the expected design displacement than columns designed to RotD50 spectra. This study presents the first step in resolving the ongoing debate over spectra definition and provides recommendations for displacement demand estimations for response spectra-based design approaches.

Direct Displacement-based Seismic Design of Glulam Frames with Buckling Restrained Braces

ABSTRACT This paper presents a direct displacement-based design (DDBD) approach for the buckling restrained braces (BRBs) braced glue-laminated timber (glulam) frame (BRBGF) structures. First, the critical design parameters of the DDBD approach were derived for BRBGFs. Then, using experimentally verified numerical models, pushover analyses and nonlinear time-history analyses (NLTHAs) were conducted on a series of one-storey BRBGFs to calibrate the stiffness adjustment factor λ for BRB-timber connections and the spectral displacement reduction factor η. Finally, the DDBD approach was verified as a prospective approach for the seismic design of multi-storey BRBGF buildings by NLTHAs of the case study buildings.

Seismic force demand on RC shear walls for direct displacement‐based design

AbstractThis article aims to investigate seismic force demand on RC shear walls which are designed using direct displacement‐based design (DDBD) method. For this purpose, first 12 shear walls were designed using DDBD approach and then were modeled nonlinearly in OpenSees using fiber section elements. Each wall was subjected to 45 artificial ground motions and the seismic force demand, including the shear force and the bending moment, were determined along the wall height. The nonlinear dynamic analysis results indicated that the seismic force demand was significantly amplified relative to the design forces. This amplification, which was due to the higher mode effects, is mainly a function of structural period and ductility demand. To find new shear and moment envelopes for capacity design, two envelop shapes compatible with internal force pattern along the wall height were selected. Then, the required equations were presented for envelope parameters based on the regression analysis of the results. The comparison of seismic force demand with proposed and previous envelopes indicates the superiority of new proposed envelopes for DDBD approach.

Direct displacement-based design approach for isolated structures equipped with supplemental fluid viscous damper

In this paper, direct displacement-based design (DDBD) approach is extended for the isolated structures equipped with supplemental fluid viscous damper (FVD) while this method can be also implemented for the isolated structures without supplemental FVD. The design process has been developed based on a non-iterative manner whereas a complexity from preliminary design to iterative design process can be found in previous DDBD approaches. To validate the proposed method, three steel moment-resisting frames with four, eight and twelve stories are designed using this method. Nonlinear time-history analysis has been performed under a far-field record set including twenty-two earthquakes and a near-field record set including fourteen earthquakes. The results show that the isolated frames without supplemental FVD have effective performance under far-field earthquakes. Therefore, the proposed design method can be employed as effective design approach for isolated structures. However, their performance is not very reliable under near-field earthquakes because base isolation system originally does not have effective performance under near-field earthquakes. Seismic performance of isolated frames equipped with FVD shows that their peak response is less than target drift under both far-field and near-field earthquakes and these frames have effectively achieved the desired performance levels related to both superstructure and base isolation levels. Therefore, the developed DDBD approach can be introduced as an effective design method for isolated structures equipped with supplemental FVD.

Development of DDBD for steel MRFs using inelastic response-based seismic lateral force distribution

Direct displacement-based design (DDBD) method is known as an effective performance-based design approach. Although this design method is theoretically stronger than force-based design approach, some previous studies reported the inability of this method to effectively achieve the design performance level. In this study, an improvement of DDBD is proposed for steel moment-resisting frames (MRFs) while the seismic design lateral force distribution is based on the inelastic response of structures. To validate its effectiveness, the steel MRFs with different heights of 4, 8 and 12 stories are designed using this modified DDBD to achieve life safety performance level under seismic hazard having 10 % exceedance probability in 50 years. The nonlinear time history analysis of these frames has been performed under twenty-two earthquake records. The results show the inability of previous DDBD to achieve the desirable performance level whereas the modified DDBD approach has effectively achieved the design performance level. All plastic hinges have been also formed in desirable locations whereas the previous DDBD approach is not quite successful in achieving this goal. The results also show that the elimination of strength-reduction factors from design process of DDBD makes drift ratio and story shear close to target drift limit and design shear. • Inability of current DDBD to achieve design performance level in steel MRFs. • Distribution of seismic lateral force based on inelastic response to improve DDBD. • Location of plastic hinges in steel MRFs designed using DDBD. • Effect of strength-reduction factors on effectiveness of DDBD.

Seismic design of self-centering viscous-hysteretic devices used for steel moment-resisting frames

A force-based design (FBD) approach is proposed for steel moment-resisting frames (MRFs) with self-centering viscous-hysteretic devices (SC-VHDs) and numerical analysis is conducted on steel MRFs with SC-VHDs designed by the proposed FBD approach. The results indicate that all of these frames satisfy the peak and residual drift criteria under the design basis earthquake (DBE) and the column-to-beam strength ratio should be equal to or more than 1.8 for frames below 8 stories, whilst for frames with 8 stories or more the column-to-beam strength ratio should be equal to or greater than 1.5 to achieve the strong column-weak beam mechanism. Considering the effects of the column-to-beam strength ratio, the seismic intensity, the structural geometric characteristics, and the parameters of the SC-VHD, inelastic displacement profiles of steel MRFs with SC-VHDs are developed. Based on the proposed displacement profiles, a direct displacement-based design (DDBD) approach is proposed for steel MRFs with SC-VHDs, and the effectiveness of both the proposed DDBD approach and the displacement profiles are verified by conducting numerical analysis on steel MRFs with SC-VHDs designed by the proposed DDBD approach.

An improvement of direct displacement-based design approach for steel moment-resisting frames controlled by fluid viscous dampers

Direct displacement-based design (DDBD) method is one of the most effective methods for performance-base design of structures that has been also employed to design structures controlled by fluid viscous damper (FVD). In previous studies, a modified DDBD has been developed to apply the higher mode effects as well as difference between spectral velocity and pseudo-spectral velocity on the design velocity of FVD. To this end, two constants were defined to correct the damping coefficient of FVD that these correction constants had been determined in a non-classical and iterative manner. In this study, a new classical method is proposed for determining these constant such that no iteration is required in DDBD. In order to be able to introduce this design approach as a reliable framework, its performance is validated under different sets of earthquake records and this design approach is also developed for structures controlled by nonlinear FVD. Steel moment-resisting frames with different numbers of stories have been designed using this method. For comparison, structures have been also designed based on DDBD proposed in previous researches. The results show that DDBD approach improved in this study is capable to achieve the design performance level under different sets of earthquake records and this design approach has more effective performance than previous design methods. Performance of steel moment-resisting frames equipped with nonlinear FVD also shows excellent performance of this design approach in achievement of desirable performance level. Therefore, DDBD approach proposed in this study can be introduced as a new classical and reliable framework because of its simplicity and excellent performance under different sets of earthquakes.

Efficient direct displacement-based seismic design approach for structures with viscoelastic dampers

Viscoelastic damper (VED) is one of most effective structural control techniques, because it provides both additional stiffness and damping to the structures. Current seismic standards implement force-based methods for the design of VEDs, which generally require extensive iterative calculations. It also causes inconsistent risk degree and economic efficiency because it is displacements, rather than forces, that are directly related to structural damage. In the past decades, researchers have developed a direct displacement-based design (DDBD) methodology. The DDBD approach begins with selecting a target displacement and estimating of the equivalent damping ratio, and then calculate the seismic demand of the structure using a substitutive equivalent elastic system. However, because of the strong nonlinearity of the VED devices, it is difficult to appropriately proportion the key parameters (i.e., damping, period) of the VED controlled structure system, which makes the DDBD method ineffective. To solve this problem, this paper proposed an efficient DDBD approach that is in accordance with the Chinese seismic design principles. The relationship between the equivalent damping and structure period of the VED-structure system is established, so the proposed approach requires minimum iterative calculations and the efficiency improves significantly. A step-by-step description of the approach is presented, in which the two key VED parameters, namely the strain amplitude and its additional damping ratio contribution to the structure, are determined by the target displacements. The approach is further examined and verified by a 24 story building. Nonlinear history analysis results confirm that, by using the proposed DDBD procedure, the designed target story drift is achieved with no iterative calculations and the structural responses of the VED-structure system satisfy the code requirements.

Investigating the effects of span arrangements on DDBD-designed RC buildings under the skew seismic attack

This paper focuses on examining the effects of span arrangements on displacement responses of plan-symmetric RC frame buildings designed using the direct displacement-based design (DDBD) method by employing non-linear analyses and the skew seismic attack. In order to show the desired performance of DDBD design approach, the force-based design approach is also used to examine the seismic performance of the selected structures. To realize this objective, 8-story buildings with different plans are selected. In addition, the dynamic behavior of the structures is evaluated by selecting 3, 7, and 12-story buildings. In order to perform non-linear analyses, OpenSees software is used for modeling buildings. Results of an experimental model are used to validate the analytical model implemented in OpenSees. The results of non-linear static and non-linear dynamic analyses indicate that changing span arrangements does not affect estimating the responses of structures designed using the DDBD approach, and the results are more or less the same. Next, in order to apply the earthquake in non-principle directions, DDBD structures, designed for one-way performance, are designed again for two-way performance. Time history analyses are performed under a set of artificial acceleration pairs, applied to structures at different angles. It is found that the mean maximum responses of earthquakes at all angles have very good agreement with the design-acceptable limits, while the response of buildings along the height direction has a relatively acceptable and uniform distribution. Meanwhile, changes in the span arrangements did not have a significant effect on displacement responses.

Drift and Response Reduction Factor of RC Frames Designed with DDBD and FBD Approach

Performance-based seismic evaluation of 2-, 4-, 8- and 12-story RC frames designed using direct displacement-based design (DDBD) and convectional force-based design (FBD) approach as per Indian standards is carried out. The DDBD approach is implemented for the design of RC frames using IS 1893 spectrum. The capacity curve and the performance point of designed RC frames are obtained by analyzing frames using nonlinear static pushover analysis. The response reduction (R) factor of designed RC frames as per FBD and DDBD method is evaluated from the bilinear idealization of capacity curve. The designed moment resisting RC frames are analyzed using nonlinear time-history analysis (NLTHA) to investigate the damage index in the form of lateral drift profile. Comparison of the NLTHA results in terms of inter-story drift ratio (IDR) and nonlinear static analysis results in terms of performance point and the response reduction (R) factor for RC frame buildings indicates the efficiency of the DDBD approach. The values of ‘R’ factor of RC frames designed with DDBD approach are observed higher than that of similar frame designed using FBD approach, indicating higher dissipation of energy through the nonlinear behavior of DDBD frame. The result shows that the building height is a crucial parameter affecting the ‘R’ factor of RC frame. The RC frames designed with DDBD approach are observed comparatively economical as compared to designed using FBD approach. The IDR of RC frames designed with DDBD approach is observed relatively higher than that of similar frames designed with FBD approach.

Performance assessment of RC frame designed using force,displacement & energy based approach

Force based design (FBD) approach is prevalent in most of the national seismic design codes world over. Direct displacement based design (DDBD) and energy based design (EBD) approaches are relatively new methods of seismic design which claims to be more rational and predictive than the FBD. These three design approaches are conceptually distinct and imparts different strength, stiffness and ductility property to structural members for same plan configuration. In present study behavioural assessment of frame of six storey RC building designed using FBD, DDBD and EBD approaches has been performed. Lateral storey forces distribution, reinforcement design and results of nonlinear performance using static and dynamic methods have been compared. For the three approaches, considerable difference in lateral storey forces distribution and reinforcement design has been observed. Nonlinear pushover analysis and time history analysis results show that in FBD frame plastic deformation is concentrated in the lower storey, in EBD frame large plastic deformation is concentrated in the middle storeys though the inelastic hinges are well distributed over the height and, in DDBD frame plastic deformation is approximately uniform over the height. Overall the six storey frame designed using DDBD approach seems to be more rational than the other two methods.

Comparing the performance of traditional shear-wall and rocking shear-wall structures designed using the direct-displacement based design approach

Reinforced concrete shear walls are widely used as lateral load resisting systems because of their favorable characteristics that include high strength, stiffness, ductility and energy dissipation. In most instances, these systems rely on the activation of a flexural mechanism at their base, where substantial damage is expected. Base-rocking systems have been proposed as a way to address this issue, mitigating severe structural damage while still limiting the seismic demands experienced by the structure. However, even when the base moment is limited, structural forces, moments and accelerations along the height of the structure can increase significantly because of higher mode effects. While this holds true for both traditional and rocking shear wall structures, past studies have suggested that rocking systems may be more prone to attract higher seismic demands. This article evaluates the performance of a set rocking shear wall structures against that of traditional reinforced concrete wall systems. The case study structures are analyzed via non-linear time history analyses, under a suite of spectrum compatible ground motions. The results of the numerical analyses confirm that while the overall performance of the rocking systems is superior to that of the “equivalent” traditional wall structures, they tend to be subjected to somewhat higher peak seismic demands.

Displacement profile for displacement based seismic design of concentric braced frames

The direct displacement based design (DDBD) procedure is well developed and used for designing reinforced concrete and steel moment resisting frame structures, wall structures and bridges. However, a limited number of studies is available on designing steel concentric braced frame (CBF) structures using DDBD approach. Moreover, those studies use the design displacement profile proposed for the reinforced concrete moment resisting frame structures by Priestley et al. (2007). Furthermore, Wijesundara et al. (2018) have highlighted that higher interstorey drifts can be observed in CBFs during the inelastic response due to the effects of higher mode amplifications. Therefore, the main objective of this study is to propose a new design displacement profile that is capable of predicting the effects of higher mode amplifications on the displacement profile for designing steel CBFs.In this regard, an attempt is made to develop a design displacement profile based on the median maximum storey displacements obtained from the nonlinear time-history analysis for a set of real ground accelerations. For this purpose, twelve different steel CBF structures with varying brace configuration, braces slenderness over the height of building, and different heights are selected. Nonlinear timehistory analyses are performed for the 3-D nonlinear finite element models of the selected frames using OpenSEES software. The developed models are capable of simulating the out-of-plane buckling. The models are subjected to a set of 30 real ground motion records with varying levels of spectral acceleration at the first modal period of the structures. The maximum storey displacement at each storey levels is recorded for all the ground motion records. On the basis of the observed storey displacement and interstorey drift, the appropriate design displacement profile for CBFs is proposed. The proposed equations show a high correlation with the observed behaviour of the suggested CBFs.

Seismic Retrofit of a Multispan Prestressed Concrete Girder Bridge with Friction Pendulum Devices

The paper deals with the proposal and application of a procedure for the seismic retrofit of an existing multispan prestressed concrete girder bridge defined explicitly for the use of friction pendulum devices as an isolation system placed between piers top and deck. First, the outcomes of the seismic risk assessment of the existing bridge, performed using an incremental noniterative Nonlinear Static Procedure, based on the Capacity Spectrum Method as well as the Inelastic Demand Response Spectra, are described and discussed. Then, a specific multilevel design process, based on a proper application of the hierarchy of strength considerations and the Direct Displacement-Based Design approach, is adopted to dimension the FPD devices. Furthermore, to assess the impact of the FPD nonlinear behaviour on the bridge seismic response, a device model that reproduces the variation of the normal force and friction coefficient, the bidirectional coupling, and the large deformation effects during nonlinear dynamic analyses was used. Finally, the paper examines the effects of the FPD modelling parameters on the behaviour of the retrofitted bridge and assesses its seismic response with the results pointing out the efficiency of the adopted seismic retrofit solution.

Displacement-Based Seismic Design Approach for Prestressed Precast Concrete Shear Walls and its Application

ABSTRACTPrestressed precast concrete shear wall (PPCW) is a new kind of shear wall utilizing a combination of unbonded post-tensioning steel and mild steel for flexural resistance across horizontal joints. A simple procedure of direct displacement-based design approach for PPCW based on concept of inelastic design spectra is proposed. Section design is then carried out according to base overturning moment. A detailed design example demonstrating a step-by-step application of the design procedure is also provided. Nonlinear time-history analysis verified that this approach is applicable to control the target displacement to the performance acceptable limit.

Seismic assessment of cold-formed steel stud bracing wall panels using direct displacement based design approach

An important advancement in structural engineering in recent years has been the development of performance-based design (PBD). However, its application to cold-formed steel framed buildings remains largely unexplored. This paper presents the assessment of the bracing capacity of cold-formed steel stud bracing wall panels using a direct-displacement based design (DDBD) approach. The fundamentals of DDBD using equivalent damping, and inelastic displacement response spectra approaches are presented. These wall parameters needed for each approach are evaluated from experimental load–deflection response behaviour under quasi-static cyclic loading. Results obtained from the DDBD approach are compared with results from conventional non-linear time history analyses (NLTHA) to confirm the validity of the adopted approach. It is found that results estimated from DDBD method using inelastic displacement response spectra approach correlated much better with NLTHA results than the equivalent damping method.

Direct Displacement-Based Design for Buildings with Hysteretic Dampers, using Best Combinations of Stiffness and Strength Ratios

A direct displacement-based design approach for damage-controlled structures using the best combination of stiffness and strength ratios between the main structure and added hysteretic energy dissipation systems is proposed. Choosing optimal values of the design parameters is an important step toward an efficient structural design; therefore, a parametric study using different combinations of design parameters is performed, from which a simple methodology to calculate a cost-efficiency index based on a cost-benefit analysis is developed. The DDBD methodology is verified and recommendations about adequate combinations of design parameters are given for an 8-story steel building with buckling restrained braces.

Two Important Issues Relevant to Torsional Response of Asymmetric 8-Story RC Building Designed with Direct Displacement based Design Approach

Direct displacement based design (DDBD) is a conceptual framework that directly design a structure to achieve an expected performance level under specified seismic intensity. In this study, two important issues relevant to torsional response of mass eccentric 8-story RC building designed with DDBD approach are investigated. These issues are including the effects of unbalanced mass distribution scenario on the torsional response parameters and the study of these parameters with reference to diagonal displacement. Diagonal displacement is the SRSS combination of the displacement demands along the direction of excitation and orthogonal direction. Three different unbalanced mass distribution scenarios which produce the same mass eccentricity were applied to the plan of the generic structural model to determine the general range of the mass moment of inertia (MMI) variation due to different unbalanced mass distribution scenarios. Expressions were established to correlate MMI and mass eccentricity in each scenario. Results show for slight eccentricities the variation of the MMI is negligible but as eccentricity is increased the range of the variation is extended. Then sensitivity analyses based on finite element method and inelastic time history analysis have been carried out on 8-story RC building frame designed with DDBD approach with different level of mass eccentricity and different MMI. Torsional response parameters in terms of maximum displacement demands of edge elements, maximum diaphragm rotation, maximum nominal relative displacement and maximum nominal rotation is compared with considering diagonal and horizontal displacement demands along seismic excitation.