Seismic Rehabilitation Research Articles

Serviceability fragility assessment of non-seismically designed railway viaducts in Turkey under near-field and far-field earthquakes

While many railway viaducts still in use in Turkish railway networks are located on active fault zones that produced historical destructive earthquakes, they are not seismically designed in accordance to current standards. This study aims to provide a better understanding about the serviceability fragility of such systems by conducting detailed probability-based seismic assessments under near-field and far-field earthquakes. To achieve this, firstly, 3D finite element models of a range of selected viaducts in Turkey were generated based on their original design drawings. The developed FE models were validated by comparing the analytical modal frequencies with the results of in-situ dynamic tests involving a series of acceleration measurements. Nonlinear time history analyses were then carried out under 25 near-field and 25 far-field real three-component ground motion recordings to obtain the seismic response of each selected viaduct. Subsequently, probabilistic seismic demand models were defined using linear regression analysis to determine relationships between engineering demand parameters (EDPs) and ground motion intensity measures (IMs). Peak ground acceleration (PGA), peak ground velocity (PGV) and spectral acceleration at 1.0 s (Sa (1.0)) were used as the IM parameter, while the maximum lateral displacement of the bridge spans for different service velocities defined in the Eurocode was considered as the EDP at serviceability damage state. Finally, analytical fragility curves for all the selected railway viaducts were developed considering maximum damage probability for the IM levels. The results, in general, demonstrate the seismic vulnerability of the existing viaducts in Turkey. It is shown that while at low speed limits the viaducts exposed to far-field ground motions were more vulnerable than those under near-field ground motions, at high speed limits the viaducts subjected to near-field ground motions were more vulnerable. Also, it is seen that reinforced concrete and masonry viaducts are generally more vulnerable to earthquakes than the steel viaducts. The outcomes of this study should prove useful for the seismic risk assessment, loss estimation and rehabilitation of the railway transportation networks in future studies.

Seismic flexural rehabilitation of RC coupling beams with FRP sheets: Evaluation of EBROG technique

Coupled shear walls (CSW) in reinforced concrete (RC) structures must be connected with stiff and strong coupling beams (CBs) to perform effectively during an earthquake. However, many RC buildings with CSW resisting systems have been designed and constructed with insufficient seismic requirements based on old codes and standards. During major earthquakes, these systems respond unsatisfactorily and may prematurely collapse. Strengthening of different RC members including CBs with fiber-reinforced polymer (FRP) sheets attached through externally-bonded reinforcement (EBR), though attractive, has always suffered from premature debonding of FRP from concrete substrate. The alternative externally-bonded reinforcement on grooves (EBROG) technique has been shown to overcome premature debonding when used instead of the EBR method. Therefore, this experimental study investigated the efficiency of rehabilitation with carbon FRP (CFRP) through the EBROG technique on the seismic behavior of flexural-deficient RC coupling beams. Furthermore, different patterns of flexural retrofit, as well as the effectiveness of FRP fans, have been studied to prevent undesirable debonding of CFRP strips. Four large-scale RC coupling beams have been identically constructed. The CB specimens were reinforced in such a way as to be flexural deficient, i.e., their loading capacities in shear were much more than that in bending. The CB specimens were then retrofitted with CFRP sheets in different patterns. The maximum peak loads of specimens CBF-1 L, CBF-1 L.F, and CBF-2 L.F increased by 37.0 %, 44.3 %, and 46.0 % over the control, respectively. Upon comparing the loading capacities of specimens CBF-1 L and CBF-1 L.F, it was found that FRP sheets installed through the EBROG method could delay premature debonding and utilize approximately 80 % of the CFRP's capacity. It was observed that using the EBROG technique and FRP fans at the termination point of FRP sheets, fully eliminated the debonding, and the full capacity of the CFRP sheets was utilized accompanied by their rupture, with improved ductility and increased load-carrying capacity of up to 46 %. It was also found that CFRP composites attached to concrete through the EBROG method significantly increased the strength, stiffness, ductility, and energy dissipation of CB specimens in terms of seismic rehabilitation.

Seismic rehabilitation of RC frames with innovative precast U-shaped UHPC jackets: Experimental evaluation and computational simulation

The rehabilitation of post-earthquake reinforced concrete (RC) frames is crucial for both restoring structural integrity and enhancing seismic resilience against future seismic events. Ultra-high-performance concrete (UHPC) is distinguished by its exceptional strength, crack-control capabilities, ductility, and durability. Despite numerous studies on its use for structural retrofitting, its application in rehabilitating damaged RC frames remains limited. This study introduced a novel precast U-shaped UHPC jacket designed for the post-earthquake rehabilitation of RC frames. The jacketing method promotes composite action in rehabilitated members through lap splicing and dowel bars, complemented by cast-in-place connections using UHPC to minimize splice length and strengthen potential weak areas under external loads. The efficacy of this jacketing approach was rigorously evaluated through cyclic loading experiments on two RC frame specimens. Results indicated that the UHPC rehabilitation method not only recovered but significantly enhanced the seismic performance of the previously damaged frame, improving initial stiffness, yield strength, peak strength, displacement ductility, and energy dissipation capacity. However, the rehabilitated frame showed a reduced yield drift and increased residual displacement compared to the as-built frame. The experimental results also revealed the necessity of accounting for bond slip in structural rehabilitation analysis and design to prevent overestimating lateral stiffness. Furthermore, the study developed a computational model that incorporates flexure, bond slip, and shear responses, aiming to effectively simulate the load-displacement behavior of rehabilitated RC frames with reasonable accuracy.

Effects of Degradation of Pipes on Seismic Rehabilitation Decision-Making for Water Distribution Networks

Effects of Degradation of Pipes on Seismic Rehabilitation Decision-Making for Water Distribution Networks

Identifying Pareto-optimal seismic rehabilitation strategies for water distribution networks considering decision maker’s risk attitudes

Identifying Pareto-optimal seismic rehabilitation strategies for water distribution networks considering decision maker’s risk attitudes

Seismic rehabilitation of existing RC school buildings with under-designed joints by means of reinforced jacketing of high performance fiber reinforced cementitious composite (HP-FRCC)

Seismic rehabilitation of existing RC school buildings with under-designed joints by means of reinforced jacketing of high performance fiber reinforced cementitious composite (HP-FRCC)

Dissipative exoskeletons for seismic rehabilitation of RC buildings

Relevant buildings like schools, public offices, assembly halls, and so on, should retain their structural integrity since their collapse could cause major human losses and significant economic impact. Moreover, such buildings should remain operational even during seismic retrofit work. This has stimulated the development of seismic retrofit solutions based on rapid, low-impact, and reversible interventions that can be done while the building is in use, removed and rapidly replaced if damaged due to earthquake, and integrated with energy efficiency measures. This situation has encouraged the use of external additive structures, commonly called exoskeletons, as a feasible solution for seismic retrofit. Typically, the research and applications deal with non-dissipative steel exoskeletons based on diagrids or external braces. This paper outlines the design and evaluation of dissipative exoskeletons. It focuses on a real school building case study, where both parallel and orthogonal exoskeleton configurations are employed. The dissipative exoskeletons are designed using a displacement-based design procedure. The effectiveness of the retrofit strategy for ductile failure modes is finally demonstrated by nonlinear time-history analyses under different sets of earthquake-ground motions.

Seismic Risk Assessment and Rehabilitation Method of Existing RCC Structures Using Micro Concrete

Aging reinforced concrete (RC) building structures typically experience more severe damage and are prone to collapse during earthquakes, constituting a primary factor in casualties and direct economic losses. To enhance the seismic performance of these old structures, this paper proposes a seismic risk assessment and a micro-concrete restoration method. It applies the process to an existing three-story reinforced concrete structure. A practical framework for mitigating structural vulnerabilities in seismic-prone regions was proposed. Then an as-built survey was conducted to create as-built architectural and structural drawings. Concrete core tests, ferroscans, and rebar tests were also performed. Based on field surveys and test data, nonlinear static and dynamic analyses have been used to evaluate structural safety. Concrete column jacketing was used to strengthen weak existing columns with micro-concrete. In assessing the structural response of retrofitted buildings, a comparison was made to their initial state. The comparison shows that applying concrete column jacketing with micro concrete can reduce other structural elements' demand capacity ratio (DCR), minimize maximum displacements, and enhance overall stiffness. The results indicate that the proposed method effectively evaluates the seismic risk of aging structures and enhances seismic resilience in existing buildings. Moreover, the application to the actual structure demonstrates that micro-concrete is highly durable and compatible with parent-concrete. Doi: 10.28991/CEJ-2023-09-12-04 Full Text: PDF

Sustainable Renovation of Public Buildings through Seismic–Energy Upgrading: Methodology and Application to an RC School Building

There are many existing buildings for which seismic rehabilitation interventions are required, especially in earthquake-prone areas like Italy. At the same time, the deep energy crisis that Europe is facing highlights the need for sustainable techniques that are able to increase the energy efficiency of buildings. In order to mitigate the social and cultural obstacles for deep renovations of buildings, effective techniques and methods are required to avoid relocating users, which often discourages such interventions. To this purpose and as the main novelty, this research is aimed at presenting a new strengthening technique for reinforced concrete buildings that is able to integrate structural seismic strengthening and energy efficiency improvements. It is made up of new framed structures connected from the outside to the existing building, thus reducing the intrusiveness and relocation needs of users. At the same time, the seismic strengthening technique is conceived for an optimal coupling with energy saving interventions like high-performance external insulation finishing systems. In this study, these techniques are described and applied to a reinforced concrete (RC) school building designed only for gravity loads, according to outdated standards. The results show that the considered strengthening technique increases the seismic performance of the building with respect to both life safety and damage limitation requirements, avoiding any further local interventions to the building’s interior. On the other hand, the energy renovation allows for significant savings, since the resulting reduction in the total non-renewable energy consumption is larger than 80%.

Comparative evaluation of seismic performance and environmental impact of traditional and dissipation-based retrofitting solutions for precast structures

Seismic rehabilitation is crucial to extend the nominal service life and help reduce the seismic losses of reinforced concrete precast industrial buildings. Along with traditional retrofitting techniques, the latest decades are witnessing a growing use of innovative solutions, the latter including devices that can dissipate the ingoing seismic energy and are characterised by the replaceability after a seismic event. The goal of this work is to compare two retrofitting solutions, respectively of traditional and innovative type, in terms of structural performance enhancement and their own life cycle environmental impact. A case study single-storey precast industrial building was retrofitted firstly adopting a traditional solution with concrete jacketing of columns, and then using two innovative energy dissipation devices, namely a friction rotation damper for beam-to-column connections and a bracing system with dissipative sacrificial elements. A comparative analysis of the seismic response of the structure in its as-built and post-retrofit configurations was undertaken, subjecting three 3D numerical models created in OpenSees to nonlinear static and dynamic analyses in both the main directions. Subsequently, two environmental impact metrics were adopted to compare the life cycle environmental impact of both the traditional and innovative retrofitting solutions, confirming that the one encompassing the dissipation-based devices is expected to be more environment-friendly, under a life cycle perspective, than the traditional concrete jacketing.

Seismic rehabilitation of URM heritage-listed Namazi school building using multiple retrofitting techniques

When dealing with retrofitting historical URM buildings, two prime aspects of their weakness against seismic action should be considered. These include: (i) the capacity of structural elements, such as foundations, masonry walls and floors, to resist earthquake forces and (ii) the integrity of the building as a whole under ground shaking. In this paper, different retrofitting techniques adopted to counter the above weaknesses in rehabilitation of the heritage-listed Namazi high school buildings are discussed. Extensive field investigations were first carried out to determine the detailed architectural and structural forms of the buildings, as well as, their material types and properties. It was found that in constructing the historic school buildings, traditional Iranian construction techniques and materials were used alongside some more modern elements such as reinforced concrete and masonry jack arch slab systems. This made the buildings unique in form, hence more challenging to retrofit. Seismic vulnerability studies were then carried out to evaluate the weaknesses of structural elements and the buildings as a whole. Different retrofitting techniques were then selected and applied to overcome the weaknesses. Effectiveness, cost and architectural constraints were the main considerations in selecting the retrofitting techniques for different parts of the historical buildings from a pool of different available methods. The techniques used in enhancing the seismic capacity of structural elements included: reinforced shotcrete overlay for masonry walls, FRP overlay for RC floors and beams, steel confinement and bracing of masonry jack arch floor systems and RC ground-beam confinement of brick and stone masonry foundations. To enhance the overall integrity of the buildings through confinement, vertical and horizontal steel tie elements and reinforced concrete tie elements were used.

Seismic behaviour assessment and rehabilitation of a masonry three‐arched bridge

AbstractMany existing historical masonry arch bridges used in the road and railway networks are still in service. However, most of them show a structural performance deficit due to several factors. This study deals with the seismic behavior assessment of an existing masonry three‐arched railway bridge through a nonlinear, non‐adaptive static analysis carried out by a three‐dimensional Finite Element model. Input data were collected from a variety of sources. The structural analysis showed a risk index that was not in compliance with the limit values suggested by current European Standards. In order to improve the structural reliability of the masonry arch railway bridge, a traditional structural rehabilitation was proposed and designed. The bottom faces of the arches and the piles of the masonry bridge were strengthened by reinforced concrete thin slabs and reinforced concrete jackets, respectively, all adequately connected to the existing structure by using steel bar connectors. Finally, a nonlinear analysis of the strengthened structure showed that the new risk index satisfied the seismic vulnerability verification. The proposed structural rehabilitation using traditional techniques appears to be a viable but not unique solution to improving structural reliability.

Design and seismic performance of precast segmental bridge columns repaired with UHPC jacket after earthquake-induced damage

Precast Segment Bridge Columns (PSBCs), which attract more attention owing to the merits of faster construction rate and higher construction quality compared with monolithic columns, are prone to serious damage under a severe earthquake. Seismic performance improvement and rehabilitation of earthquake-damaged PSBCs are significant to promote applications in seismic-prone areas. Ultra-high performance concrete (UHPC) jackets, which are promising in the field of rapid retrofit of civil structures, were used to retrofit damaged PSBCs in this study. To investigate the seismic design method and performance of repaired PSBCs using UHPC jackets, a 1/10-scale earthquake-induced damaged PSBC was retrofitted based on a proposed reinforcement design method, and tested under vertical loading and incremental lateral cyclic loading. The failure mode, hysteresis curve, residual displacement, and energy dissipation capacity of the repaired column were compared with those of the original column. In addition, based on a verified 3D finite element model by the test, a parameter analysis was conducted to explore the effect of the height and wall thickness of the UHPC jacket on the seismic behavior of the repaired PSBCs. The results indicated that the earthquake-damaged PSBC repaired with the UHPC jacket had an equivalent initial stiffness, 18.9% higher energy dissipating ability at 4.0% drift ratio and 16.2% larger strength compared with the undamaged column. The numerical simulation showed that the height and thickness of the UHPC jacket had an influence on the failure location and strength of the repaired PSBCs. Besides, the design method for the damaged precast column reinforced with the UHPC was confirmed by the test and finite element model, and it could be applied to the retrofit design of the damaged precast segment column.

Experimental Behavior of Confined Masonry Walls Rehabilitated with Reinforced Mortar Jacketing Subjected to Cyclic Loading

Results of an experimental program of 13 confined masonry walls rehabilitated with different techniques are presented. All specimens were built to full-scale with an aspect ratio (height to length) of 1. Vertical confining elements of one wall were built with 6.4 mm diameter welded wire reinforcing cages. Before rehabilitation, 11 of the 13 walls were initially tested to induce repairable damage; the other 2 were strengthened in an undamaged state. During testing, walls were subjected to a constant vertical load. Initially, damaged walls were rehabilitated using various techniques, such as jacketing made of mortar and welded wire mesh and synthetic or steel fibers. One initially damaged wall was rehabilitated with premixed mortar and fiberglass mesh. After rehabilitation, specimens were tested for failure. The experimental program is discussed, including materials characterization and main test results. Recommendations to practicing engineers involved in rehabilitating earthquake-damaged masonry structures are presented. It was found that the original capacity of the walls, in terms of strength, stiffness, and deformation, was increased considerably using the studied techniques. It is concluded that the techniques evaluated in this project are adequate for the seismic rehabilitation of masonry structures.

Modeling of shear-lap tests of flat and curved masonry specimens strengthened by FRCM

Nowadays Fiber Reinforced Cementitious Matrix (FRCM) systems play a relevant role in the context of innovative interventions for the seismic rehabilitation of masonry structures. Their capacity in improving the strength of masonry components is comparable with the one observed in case of Fiber Reinforce Polymer (FRP) systems, but with additional advantages (lower costs, environmental compatibility, removability, etc.). Nevertheless, although a relevant number of applications concerns curved structures (arches, vaults, domes, etc.), the majority of studies available in literature provide a contribution mainly concerning the specific case of applications on flat masonry substrates. The present paper is part of a research activity carried out by the Authors with the main goal to provide a contribution toward the study of the bond behavior of FRCM systems externally applied to curved masonry elements. In particular, the results of numerical analyses carried out by means of a simple modeling approach proposed by the Authors are here carried out by considering as case studies specimens object of a recent experimental investigation. Specific aspects influencing the local bond behavior of FRCM systems applied on curved masonry substrates are then analyzed by opportunely introducing them into the numerical model. The obtained results allow for understanding the effect of important features, experimentally observed in terms of global response, and here assessed in terms of local bond behavior, by particularly emphasizing the role of the curvature and the strengthening position.

Experimental Characterization, Modeling, and Numerical Evaluation of a Novel Friction Damper for the Seismic Upgrade of Existing Buildings

The paper presents the experimental characterization, the formulation of a numerical model, and the evaluation, by means of non-linear analyses, of a new friction damper conceived for the seismic upgrade of existing building frames. The damper dissipates seismic energy through the friction force triggered between a steel shaft and a lead core prestressed within a rigid steel chamber. The friction force is adjusted by controlling the prestress of the core, allowing the achievement of high forces with small dimensions, and reducing the architectural invasiveness of the device. The damper has no mechanical parts subjected to cyclic strain above their yield limit, thereby avoiding any risk of low-cycle fatigue. The constitutive behavior of the damper was assessed experimentally, demonstrating a rectangular hysteresis loop with an equivalent damping ratio of more than 55%, a stable behavior over repeated cycles, and a low dependency of the axial force on the rate of displacement. A numerical model of the damper was formulated in the OpenSees software by means of a rheological model comprising an in-parallel system of a non-linear spring element and a Maxwell element, and the model was calibrated on the experimental data. To assess the viability of the damper for the seismic rehabilitation of buildings, a numerical investigation was conducted by performing non-linear dynamic analyses on two case-study structures. The results highlight the benefits of the PS-LED in dissipating the largest part of seismic energy, limiting the lateral deformation of the frames, and controlling the increase in structural accelerations and internal forces at the same time.

Cyclic performance of severely earthquake-damaged RC bridge columns repaired using grouted UHPC jacket

The bridges constructed in high seismic zones may suffer one or more earthquake shocks of certain scales during their service life. Some of them could be severely damaged during a catastrophic earthquake event. How to quickly and economically restore bridge service functions and traffic lifelines has always been the concern of bridge owners and engineers. In this study, a method for repairing seismically damaged reinforcement concrete (RC) bridge columns using ultrahigh performance concrete (UHPC) materials was developed. Seven down-scale RC bridge column specimens with three different reinforcement ratios and two different heights were designed according to the seismic design code for RC bridges. For three of the specimens, the reinforcement around the plastic hinge area were artificially corroded through chloride ion penetration method to simulate the strength degradation effect of reinforcement erosion that could occur in many aging bridge columns. All seven specimens were tested by applying cyclic loads until their plastic hinge became severely damaged, which were then repaired following the proposed procedure and with different jacket thicknesses. The cyclic tests were re-conducted for these repaired specimens. The testing results were analyzed by comparing to those from the test for the non-seismic-damaging specimens one by one with respect to their seismic performance in order to validate the seismic rehabilitation effect using UHPC materials. Additionally, an ABAQUS software based finite element model was developed for numerically simulating the hysteretic behaviors of the columns repaired using UHPC jacket. The resulting hysteretic curves for the repaired columns with different reinforcement ratios and heights well matched those from the corresponding cyclic tests. This model can be further used for seismic performance prediction and UHPC jacket design for the repaired bridge columns that have different dimensions and reinforcement configurations. All of these experimental and analytical results show that the seismic performance of the repaired bridge columns can be effectively restored in a relatively fast and low-cost manner.

Evaluation of hybrid NSM-CFRP technical bars and FRP sheets for seismic rehabilitation of a concrete bridge pier

Seismic retrofit is a cost-effective and sustainable solution for improving bridge structures in seismic zones. Fiber Reinforced Polymer (FRP) is commonly used to replace steel components in retrofit projects due to their light weight, high strength, and high corrosion resistance. The fabrication of novel hybrid structures from FRP and concrete is the next step researchers are addressing. In this context, the present study focuses on numerical modeling of the experimentally determined response of a hybrid FRP and concrete bridge pier subjected to quasi-static tests. The results from FEM showed strong agreement with the experimental response in terms of load-displacement curve and failure mode. After validating the model, alternative designs (changing the height of the CFRP slab, changing the height and compaction of the CFRP bar, and concrete encasement with and without CFRP slab) were numerically tested to investigate the effects of each model on the load capacity. With the conventional concrete encasement, the bearing capacity of the bridge pier can be rehabilitated, but with the CFRP plate in the above system, the bearing capacity of the bridge pier is increased by more than 60%. Therefore, it can be concluded that seismic strengthening techniques with CFRP sheets and mounted NSM-CFRP bars are suitable for concrete bridge piers.

Numerical investigation on the seismic performance of a RC framed building equipped with a novel Prestressed LEad Damper with Straight Shaft

This study aims at assessing the use of a novel damper, which is called the Prestressed LEad Damper with Straight Shaft (or PS-LED), for the seismic rehabilitation of RC framed buildings. This device provides high energy dissipation by the friction activated between a lead core and a shaft and achieves a high specific output force by preloading the lead during the assembly. In order to show the effectiveness of the PS-LED device for the retrofit of existing buildings, a RC structure designed according to past codes that ignored seismic actions is retrofitted with the PS-LED system considering two different damage targets: (i) in the first case, the structure is retrofitted in order to behave elastically under the design earthquake; (ii) in the second case, a partially dissipative behavior of the structure is conceived, with activation of plastic hinges, and limited and reparable damage. In order to assess the suitability of the design procedure, non-linear static analyses are performed on the upgraded building, showing a satisfactory agreement between the seismic performance and the design target. Non-linear dynamic analyses are further carried out considering a suite of bidirectional artificial ground motions with response spectra matching on average the target spectrum according to the Italian Building Code for the life-safety limit state. Finally, a comparison is performed between the performances of the building retrofitted with the PS-LED device and the building retrofitted with a conventional steel hysteretic damper (SHD), demonstrating that the PS-LED, thanks to its superior damping capacity, limits the increase in internal forces that usually affects frames equipped with SHDs, reducing the need of local strengthening of the columns and foundations and consequently the total cost of the seismic rehabilitation.

Seismic vulnerability analysis and structural rehabilitation of a historical masonry tower

This paper presents the results of the structural performance assessment of an existing masonry tower and the subsequent repair and strengthening intervention. The study deals with an Italian architectural heritage building in the Cilento National Park (Southern Italy): the bell tower in Torre Orsaia. The tower has been the subject of on-site diagnostic investigations including geometrical surveys, laser scanning surveys, flat jack tests, endoscopic tests, sonic pulse velocity tests, geognostic surveys, and tie-rods tests. The multilevel assessment path proposed by the Italian Guidelines for the assessment and mitigation of the seismic risk of the cultural heritage is followed and the corresponding results are discussed. The global inelastic behavior of the masonry tower is studied through a macro-model approach using the nonlinear static (pushover) analysis. The local collapse mechanisms are studied through a kinematic limit analysis based on rigid block rotation. The repair and strengthening interventions have shown their effectiveness to close the existing cracks, preventing damage to the belfry, and improving the seismic performance of the tower. Both the compatibility, durability, and reversibility of the interventions and their reliability and monitoring are finally highlighted since the bell tower of Torre Orsaia is a historical heritage building.