Post-earthquake Repair Costs Research Articles

Experimental evaluation of bonded/unbonded prestressed precast concrete joints under repetitive loading scenarios: Seismic performance and retrofit intervention

Recently, demands for mitigating structural damage and post-earthquake repair costs have spurred considerable research on prestressed precast frames. In this study, quasi-static tests were conducted on bonded and unbonded prestressed precast beam-column joints (BPPJs and UPPJs) to investigate the influences of bonded/unbonded post-tensioned (PT) strands, evaluate the performance of BPPJs under repeated loading, and verify the effectiveness of post-earthquake retrofitting with external buckling-restrained rods (BRRs). Additionally, the difference between the bonded and unbonded joints was further revealed from the perspective of the tensile forces of the strands at the beamcolumn interface. Test results showed that compared with the UPPJ, the BPPJ exhibited superior performance in terms of lateral stiffness, lateral resistance, and energy dissipating capacity, with a 76.4 % increase in the load-bearing capacity. The compressive zone at the beam end was also deeper in the BPPJ, accompanied by a denser distribution of compressive cracks in the concrete. Furthermore, the bond between the strands and grouting material in the duct accelerated the increase in the tensile forces of the strands at the interface, resulting in considerably more prestress loss in the BPPJ after the tests, which was 120.0 % greater than that in the UPPJ. Under repetitive loading scenarios, although the yielding resistance of the BPPJ decreased by 35.0 % compared with that of the first loading owing to the reduced tensile forces in the strands, relatively minor variations in the load-bearing capacity and energy dissipation were observed. After retrofitting with BRRs, the BPPJ exhibited substantial enhancements in both lateral stiffness and resistance, validating the effectiveness of post-earthquake retrofitting with BRRs.

Seismic evaluation of post-tensioned precast concrete frames with non-grouted fuse-type dissipaters under successive excitations

In recent years, demands for mitigating structural damage and post-earthquake repair costs have spurred considerable research on self-centering seismic force-resisting systems. This study evaluates the Post-tensioned Precast concrete Frame with non-grouted fuse-type Dissipaters (PPFD) through experimental and numerical methods. Quasi-static tests were conducted on a one-bay, single-story PPFD to investigate its seismic response. The tested PPFD was shown to effectively control damage to concrete components and limit residual displacements; imperfections at the beam-column interface joint had a negative effect on the initial stiffness and self-centering performance of the PPFD. Parametric analyses were then performed to discuss the force and deformation responses of the beam-column joint in the PPFD with dissipaters solely beneath the beam. A design method for the PPFD was developed based on the formulas derived and verified from the parametric analyses. Nonlinear dynamic analyses were then employed to evaluate prototype designed multi-story PPFDs subjected to individual earthquakes in addition to mainshock-aftershock sequences. The findings indicated that both configurations of PPFD, with dissipaters either symmetrically arranged on the beam or located exclusively below the beam, exhibited comparable maximum inter-story drifts and significantly smaller residual inter-story drifts than a comparable reinforced concrete frame. Moreover, the PPFD demonstrated only a minor increase in both the maximum and residual inter-story drifts when subjected to aftershocks, compared to a much larger increase for the reinforced concrete frame.

A Novel Hybrid Self-Centering Piston-Based Bracing Fitted with SMA Bars and Friction Springs: Analytical Study and Seismic Simulation

Self-centering piston-based braced frames (SC-PBBFs) are such structural assemblies that can withstand a severe earthquake through passive control. The self-centering motion of the bracing system curtails the seismic permanent damage of a building, thereby considerably mitigating postearthquake repair costs and downtime. This paper proposes a novel hybrid self-centering piston-based bracing (SC-PBB) equipped with friction springs (FS) and superelastic shape-memory alloy (SMA) bars. Analytical formulas are presented for rapid analysis and preliminary seismic design of the SC-PBBFs fitted with SC-PBBs. The general mechanics of the proposed archetypes confirms their symmetric self-centering behavior. To validate the proposed design procedure, a set of SC-PBBFs fitted with tension-only SMA bars and precompressed FS is examined under far-field ground motions. Effects of prestressing of components and earthquake types (crustal, subcrustal, and subduction) are quantified and compared with the responses of buckling-restrained braced frames (BRBFs). The analysis outcomes revealed the effectiveness of the proposed hybrid SC-PBBF subjected to design-level earthquakes.

Experimental investigation and seismic analysis of a novel self-centering piston-based bracing archetype with polyurethane cores

This paper introduces a novel self-centering Piston-based Bracing with Polyurethane Cores (PBPC) as a passive seismic control device. Frames fitted with such bracing elements will be able to mitigate the loss of life, post-earthquake repair costs, and downtime recovery after a major seismic event. The proposed earthquake-resistant archetype integrates a steel shaft, steel tubes, and hollow and solid polyurethane (PU) cylindrical cores. The PU cylinders are activated using a bracing shaft and dissipate seismic energy with a self-centering response. A set of unidirectional cyclic tests were conducted on a scaled PBPC specimen to quantify the effects of pre-compression force level, loading rate, and past loading history. The pre-compressed force curtailed the undesirable viscoelastic deformation and the energy dissipation capacity of PU cores. The non– and pre-compressed PBPC elements exhibited large deformability and adequate energy dissipation; nonetheless, they recovered their initial conditions with stable flag-shaped hysteresis loops following successive compression cycles. Additionally, a new material model was developed in OpenSees software for PBPC and a comparative seismic analysis was conducted. The simulation outcomes supported by experimental data proved the efficiency of the frame fitted with PBPCs in mitigating damage compared with a buckling-restrained braced frame.

Determination of optimal behavior of self-centering multiple-rocking walls subjected to far-field and near-field ground motions

In recent years, innovative seismic resistant systems have been introduced based on the Damage Avoidance Design (DAD) philosophy rather than the conventional plastic design-based methods to reduce damages to buildings and to decrease post-earthquake repair costs. Self-centering multiple-rocking walls are amongst these innovative systems. This study aims to determine the optimum number of rocking sections in self-centering concrete multiple rocking walls. To this aim, the seismic behavior of self-centering (SC) concrete rocking walls of 8, 12, 16, and 20 stories with different numbers of rocking sections were examined. Several non-linear time-history analyses were carried out via OpenSEES software in a two-¬dimensional framework. Three sets of ground motions were considered including 22 Far-Field (FF), 14 Near-Field-Pulse (NFP), and 14 Near-Field-no Pulse (NFnP). Five types of quad-rocking walls and one type of dual-rocking walls were specified and compared with base-rocking walls and fixed-base walls. To perform this comparison, a set of utility coefficients was defined to integrate different response aspects including shear and moment demands as well as the residual drifts. The results showed that the effects of higher modes (shear and moment demand) increase with the increase in the height of the rocking structures. Furthermore, NFnP and FF records produced higher mode effects in rocking systems as compared to NFP records. The results suggested that the quad-rocking walls with the reduced tendon area in the first block (R4-S1) are highly effective in reducing the effects of higher modes in NFP and NFnP records. They showed maximum utility coefficients of 67% and 65%, respectively. Also, quad-rocking walls with the reduced tendon area in the third block (R4-S3) were more effective under FF records and their maximum utility coefficient was 65%. The residual roof drift of rocking walls was so negligible that its maximum value in the 8-story structure under NFP records was 0.0008.

Seismic performance of self-centering steel-timber hybrid shear wall structures

This paper presents the seismic performance assessment of self-centering steel-timber hybrid shear wall (SC-STHSW) structures. The hybrid structure introduces extra re-centering action to itself through the combination of the post-tensioned steel frame (PTSF) with the light-framed wood shear wall. Slip friction dampers (SFDs) are used as connectors between the frame and the wood wall. An OpenSees model for the SC-STHSW was established and validated versus experimental results. Then, a 9-story SC-STHSW structure was designed with the direct displacement-based design procedure, and the design was checked through nonlinear time history analysis. Based on the designed 9-story SC-STHSW structure, the influence of a key parameter (i.e., self-centering ratio α E ) on the structure's dynamic performance was investigated by considering different hazard levels. The dynamic response of three 9-story SC-STHSW structures with different α E values was compared in terms of maximum inter-story drift (MaxISD) and maximum residual inter-story drift (MaxRISD). Meanwhile, the fragility curve of a 9-story conventional steel-timber hybrid shear wall (STHSW) structure without self-centering capability was calculated based on the cloud analysis, and the fragility curves were compared with those of the 9-story SC-STHSW. It was found that the increase of α E was not only beneficial to decrease the system's MaxRISD but also positive in enhancing system's control over its MaxISD. The lower limit of α E was suggested to be 0.6 when the system was used in high seismic regions. The 9-story SC-STHSW ( α E = 0.6) was comparable to the 9-story STHSW system in regards to the control of MaxISD, which illustrated the advancement of the new system since, at the same time, it had better re-centering ability to decrease post-earthquake repair costs. • A self-centering steel-timber hybrid shear wall structure was designed through the direct displacement-based design. • The influences of α E on the new structure’s seismic performance were explored. • Based on cloud analysis, the seismic fragility of the new structure was compared with the other structure.

BIM-based approach for the cost-optimization of seismic retrofit strategies on existing buildings

Abstract Building Information Modelling (BIM) is a digital representation of the physical and functional characteristics of a facility and is used to manage an entire construction process (design, construction and management across the entire lifecycle). BIM can be regarded as both a digital representation of a building and a store of data with which to facilitate interoperability and the exchange of information throughout the lifecycle of a structure. Buildings sustain economic losses during their lifecycle due to ordinary maintenance operations and unpredictable events. These events reduce the structural performance of a building and highlight the need for financial investment. The costs of maintenance operations are usually accurately defined, but other expenditure is not as easy to evaluate when events are uncertain. A lifecycle cost (LCC) analysis of buildings exposed to seismic risk is a critical issue in structural engineering. Expected losses, including initial and post-earthquake repair costs, are an important parameter in structural design. Herein, a simplified method based on a semi-probabilistic approach is implemented in a BIM model to evaluate the economic performance, and economic losses, of a building exposed to seismic risk. A BIM procedure is implemented in a case study to improve the feasibility of this process and to deal with the large amount of data concerning the damage to and cost analysis of the components that constitute the facility. Furthermore, this specific BIM tool for the economic loss assessment has been embraced in a wider methodology aimed at optimizing the seismic retrofit strategy, taking into account both safety and economic features.

RETRACTED ARTICLE: Estimation of Load-Induced Damage and Repair Cost in Post-Tensioned Concrete Rocking Walls

Post-tensioned concrete rocking walls might be used to avoid severe seismic damage at the base of structural walls, decrease residual drift, and lessen post-earthquake repair costs. The prediction of load-induced damage to the rocking wall resulting from seismic loading can provide an extremely valuable tool to evaluate the status and safety of structural concrete walls following earthquakes. In this study, the behavior and the damage state of monolithic, self-centering, rocking walls, as a new type of concrete rocking wall, are investigated. The nonlinear mechanical behavior of the wall is first modeled numerically, and subsequently the mechanical parameters from the numerical simulation are used to generate the local damage index. The results from the damage index model are compared with the full-scale test results, confirming the viability of the numerically based damage index method for estimating the seismically induced damage in concrete walls. Moreover, the estimated damage can be utilized as a qualitative and quantitative scale to assess the status of the wall following seismic loading events. Finally, an equation is proposed to estimate the repair cost based on the predicted damage state for the studied structural system.

Passive self-centering hysteretic damping brace based on the elastic buckling mode jump mechanism of a capped column

Traditional civil structures with yielding systems can be subjected to damage and permanent deformation through major earthquakes, which may induce substantial post-earthquake repair costs and is a critical issue for performance-based seismic design. A novel capped column with an elastic buckling mode jump (BMJ) mechanism is introduced as an economical passive alternative for obtaining flag-shaped hysteretic damping, self-centering and reusability in seismic design. A simple analytical model for the BMJ mechanism is derived and verified with finite element model simulation results for a variety of capped column geometric configurations. Using the validated analytical model, a parametric study is conducted on the geometric properties to provide design guidance. A practical passive self-centering hysteretic damping brace design is also provided in this paper, based on a combination of multiple BMJ mechanisms. The seismic performance of a 3-story frame building under a suite of 20 earthquake ground motions with BMJ brace is compared with a buckling-restrained brace (BRB) frame system as well as a conventional brace (CB) frame system. The results demonstrate the potential of a brace system utilizing BMJ mechanisms to outperform BRB and CB by achieving acceptable inter-story drift response without sustaining residual drift.

Multi-criteria optimization of lateral load-drift response of posttensioned steel beam-column connections

Posttensioned (PT) elements in steel buildings can substantially mitigate permanent seismic damages and the associated post-earthquake repair costs during earthquakes. In this paper, a response surface methodology (RSM) is used to predict and optimize the lateral response characteristics of PT steel beam-column connections with top-and-seat angles. The monotonic lateral response characteristics considered in the study include: initial stiffness, load capacity, and ultimate drift of PT connections, as well as load and drift levels corresponding to the gap-opening (decompression) in PT connections. Based on the results of finite element simulations and extensive sensitivity studies, six influential parameters are considered as input variables in this study. These parameters are posttensioning strand force, beam depth, beam flange thickness and width, span length, and column height. By using a desirability approach, the lateral response of PT steel beam-column connections is optimized. The optimization studies aim at maximizing the initial stiffness, load capacity, and ultimate drift of PT connections and/or minimizing the amount of steel in the beam section, which contributes to the final cost of frame structures. The multi-criteria optimization studies reveal the regions of factor space where optimal conditions are achieved. The optimized solutions are then confirmed by performing simulation runs with the optimal factor combinations. Among the results, it is shown that damage occurs earlier in PT connections with deeper beams and greater posttensioning strand forces. The dominant limit state for the PT connections was beam local buckling starting at early drifts of 1.2%, whereas the first occurrence of angle fracture was at about 4% drifts, and two limit states of strand yielding and bolt extensive yielding were not observed in the analyzed PT connections.

Optimising portfolio loss reduction using a first-order reliability method sensitivity analysis

Advancements in loss estimation methodologies for building portfolios provide an opportunity for pre-disaster risk mitigation, particularly through structural retrofit. Budget constraints, however, limit which vulnerable buildings within a region are to be retrofitted to desirable levels of seismic resistance. This paper presents a new reliability-based approach to prioritise retrofit strategies to support regional earthquake risk mitigation efforts. The proposed framework uses the first-order reliability method (FORM) to evaluate a probability distribution of repair costs for a suite of spatially distributed buildings. Sensitivity measures computed within the FORM analysis are paired with retrofit costs. The proposed method is applied to a San Francisco neighbourhood building inventory, and results suggest which building categories should be upgraded to minimise estimated post-earthquake repair costs. The importance of spatial correlation as well as the level of loss to be minimised is investigated relative to cost-effective retrofit spending.

Evaluating and Upgrading Welded Steel Moment-Frame Buildings Using FEMA-351

In July 2000, the SAC Joint Venture (a joint venture of the Structural Engineers Association of California, the Applied Technology Council, and California Universities for Research in Earthquake Engineering) prepared a series of recommendations regarding welded steel moment-frame design, evaluation, and upgrade procedures. FEMA-351, Recommended Seismic Evaluation and Upgrade Criteria for Existing Welded Steel Moment-Frame Buildings, was developed to evaluate the probable performance of existing steel moment-frame buildings in future earthquakes and to provide guidance or upgrading these buildings. The procedures introduced in FEMA-351 allow the determination of the level of confidence a structure will be able to achieve based on a specified performance objective, using simplified analytical methods. Simplified procedures for estimating the probable post-earthquake repair costs and nonstructural damage, based on the losses incurred in the 1994 Northridge earthquake, are presented as well. This paper provides a brief chapter-by-chapter overview of the information contained in FEMA-351 and emphasizes the performance evaluation procedures by stepping through the process using an example building.