Seismic Strengthening Research Articles

Experimental assessment of proposed seismic strengthening scheme for adobe structures

A new scheme of seismic strengthening of adobe structures has been proposed in this paper. The scheme involves horizontal and vertical bands of steel wire mesh plastered with cement-sand mortar. The effectiveness of the proposed scheme is assessed by dynamically testing a half-scale model of the adobe structure on a shaking table. The acceleration time history record of the 1995 Kobe earthquake was used to simulate the ground motion for the strengthened model which was increased sequentially in increments of 25% of peak ground acceleration (PGA). Initial (hairline) cracks were observed in the in-plane wall of the model at a PGA of 0.439 g. Although the out-of-plane walls also sustained damages, the in-plane walls were the most damaged parts of the structure. The proposed strengthening method reduced the torsional irregularity of the structure. It also increased strength, ductility and energy dissipation capacities of the walls. The data of observed structural damages and building drift were used to propose four performance levels for the strengthened adobe structures corresponding to the applied PGAs of ground motion.

In-plane behaviour of masonry walls embedding with steel welded wire mesh overlay with mortar

ABSTRACT This paper presents an experimental study of the structural behaviour of masonry walls strengthened with steel-welded wire mesh (WWM) overlay with mortar to improve their in-plane shear strength and deformation capacity. The experimental programme consists a compression testing of masonry prism and a diagonal compression testing of 15 wall specimens made of clay brick strengthened with four different WWM systems: (i) embedding WWM along the bed joint, (ii) embedding WWM along the bed joint and a strip diagonally crossing on wall surface, (iii) WWM alternately embedding along the bed joint and continue to the surface of wall and (iv) WWM fully cover on wall surface. The experimental results show that the adopted WWM-strengthening solutions produce a beneficial increase of compressive strength, shear resistance, ductility and energy dissipation capacity making them suitable for seismic strengthening.

Experimental Evaluation of Brick Masonry Walls Strengthened with TRM (Textile Reinforced Mortar) Renders

Old masonry buildings, which are frequently part of the cities-built heritage, are vulnerable to seismic actions. Thus, it is important to conduct efficient seismic strengthening interventions that allow maintenance of the existing building to minimize the environmental and economic impact. The use of reinforced renders is a simple and effective solution for seismic strengthening of this type of constructions. In this paper, several compositions of reinforced renders are analyzed, consisting of mortars with air lime, hydraulic lime, or cement binders, reinforced with steel mesh, fiberglass mesh and a natural fiber mesh. Additionally, the results of diagonal compression tests on three small wall specimens are presented, one of which is non-reinforced and the other two are strengthened with reinforced renders. The results of all tested walls are presented and compared, allowing us to evaluate the efficiency of the reinforced render on the wall shear strength.

Research on Seismic Design and Strengthening of Modern Building Structure

Research on Seismic Design and Strengthening of Modern Building Structure

Seismic strengthening of existing RC buildings with external cross-laminated timber (CLT) walls hosting an integrated energetic and architectural renovation

In this study a timber-based integrated solution is presented to solve at once common issues affecting typical reinforced concrete (RC) existing buildings, such as seismic and energy performances, providing an eco-friendly alternative to steel external bracing systems. Cross-laminated timber (CLT) walls are provided perpendicularly to the external façades as strengthening elements while interposed CLT slabs are foreseen at each floor level to host new architectural units together with a new envelope. While the connections to the foundations and to the existing RC frames are provided respectively with steel brackets and axial-connectors distributed along the height of the building, a post-tensioned connection, between CLT panels (PT-CLT connection), is implemented in the system to guarantee resistance to horizontal actions acting parallel to existing façades with consequent structural independence and architectural freedom. On this regards a first look at the findings of an experimental campaign carried on the Technical University of Munich are presented. A numerical model is developed with finite element software characterizing each type of connector for linear and non-linear analyses. Modal analyses with response spectrum are performed to verify structural elements and connectors, while pushover analyses with target displacement checks are performed to assess the obtained seismic improvement. Finally, the preassembled architectural components that allow to renovate the envelope and the provided assembly procedure are revealed.

In-Plane Seismic Strengthening of Brick Masonry Using Steel and Plastic Meshes.

Unreinforced masonry structures are vulnerable to seismic loading due to their brittle behavior, and must therefore be strengthened. This paper presents the seismic performance of brick masonry strengthened with steel and plastic meshes. For this purpose, twenty masonry wallets of (600 × 600 × 113 mm) were constructed, keeping the same materials and workmanship. Fifteen of them were reinforced using steel and plastic meshes. These specimens were tested for in-plane static cyclic diagonal tension (shear) behavior. The critical parameters, such as shear stress, strain, failure modes, ductility, energy dissipation, and stiffness degradation were investigated. Compared to reference and plastic-reinforced specimens, the steel-reinforced samples were found to be highly effective. Furthermore, the recommended category of steel increased the shear capacity, energy dissipation, and ductility ratio by 1.3, 14, and 6.3 times, respectively.

Tectonic Influence on the Geomorphology of Submarine Canyons: Implications for Deep-Water Sedimentary Systems

A database-informed metastudy of 294 globally distributed submarine canyons has been conducted with the aim of elucidating the role of tectonic setting on submarine-canyon geomorphology. To achieve this, data from seafloor and subsurface studies derived from 136 peer-reviewed publications and from open-source worldwide bathymetry datasets have been statistically analyzed. In particular, relationships between margin type (active vs. passive) or plate-boundary type (convergent vs. transform vs. complex) have been assessed for key morphometric parameters of submarine canyons, including: streamwise length, maximum and average width and depth, canyon sinuosity, average canyon thalweg gradient, and maximum canyon sidewall steepness. In addition, possible scaling relationships between canyon morphometric parameters and characteristics of the associated terrestrial catchment, continental shelf and slope, and of the broader physiographic setting for canyons along both active and passive margins have been evaluated. The following principal findings arise: 1) overall canyon geomorphology is not markedly different across tectonic settings; 2) slope failure might be more important in passive-margin canyons compared to active ones, possibly due to seismic strengthening in the latter; 3) some aspects of canyon geomorphology scale with attributes of the source-to-sink system and environmental setting, but the strength and sign in scaling might differ between active and passive margins, suggesting that the extent to which canyon geomorphology can be predicted depends on the tectonic setting. Insights from our analysis augment and improve conceptual, experimental and numerical models of slope systems at the scale of individual canyons and source-to-sink systems, and increase our understanding of the complex role played by tectonic setting in shaping deep-water systems.

Study on the seismic performance of rural houses masonry walls with different geometries of open-hole area reduction

Masonry houses account for 90% of all rural houses in China, which is of great practical significance for studying the seismic strengthening of masonry houses. Based on the actual structural forms of existing farm houses in Beijing, this paper proposes a cost-effective reinforcement scheme using additional masonry walls with different geometries to strengthen the open-hole brick walls to fulfill the seismic protection requirements. The open-hole masonry walls were examined and compared in load–displacement, hysteresis curve, skeleton curve, ductility, energy consumption, and stiffness degradation through quasi-static tests and finite element analysis. The test results were verified by finite element analysis. In addition, the reinforcement effect was verified regarding damage characteristics, hysteresis curves and skeleton curve trends. Compared to the unreinforced wall, the wall reinforced by adding 740 mm to one side of the open brick window increased the ultimate bearing capacity by 136% and the damage displacement by 56%. By adding 370 mm to one side of the open-hole brick masonry window, the ultimate bearing capacity increased by 83%, and the damage displacement increased by 10%. Furthermore, by adding 370 mm of wall symmetrically along both sides of the open-hole brick masonry window, the ultimate bearing capacity increased by 185% and the damage displacement increased by 67%. These results indicate that the reinforcement technique can effectively improve the lateral stiffness and seismic performance of the open-hole masonry walls. In addition, the formula for calculating the seismic bearing capacity of open-hole walls reinforced with masonry walls is also proposed.

Effectiveness of unreinforced masonry seismic retrofit programmes: review of policies in New Zealand and the United States

Implementing seismic risk mitigation programmes for earthquake-prone unreinforced masonry buildings (URM) is critical to ensure public safety and community resilience in regions of moderate and high seismicity. In New Zealand, it is a mandatory requirement to strengthen earthquake-prone buildings within a prescribed timeframe. However, the rate of compliance has been slow. Building owners delay or hesitate to undertake seismic strengthening, mainly due to uncertainties involved in cost (Egbelakin et al., 2014) [1]. While cost is the pivot of the owner's decision-making process, an effective design of government-led programmes is essential to engage the owners and increase the rate of compliance. This paper compared similar mandatory URM programmes in the United States and New Zealand to identify critical contributors to the success of each programme. In addition, this paper implements a regression analysis using actual remediation cost data gathered from a recent mandatory strengthening programme in New Zealand to identify significant cost factors in seismic strengthening. From the comparison, six key contributors to programme success were recognised, including 1) efficient and flexible financial options; 2) alternative retrofit design solutions; 3) fair penalties and enforcement tools; 4) a clearly laid out action plan and time limits for compliance; 5) dedicated local council staff and case managers; 6) consultation with building owners. The cost model suggested that building characteristics, location, and heritage status are significant in seismic strengthening costs. The findings contribute to the fine-tuning of future programme designs and the understanding of financial impediments building owners face in seismic strengthening. Significant cost factors identified in this study indicate where the allocation of government funding is required the most to maximise the incentivising of owners for early adoption of compliance measures.

Metoda projektiranja i inženjerska primjena posmičnih zidova s tarnim prigušivačem seizmičke energije

At present, the target of seismic strengthening is to gradually work towards the objective of being able to quickly restore function, and even replace function after an earthquake. In addition, the foot of reinforced concrete shear walls is easily damaged in shear wall structures. If a damper is set in this part, it can ensure the normal stiffness and energy consumption function of the shear wall, and it can be easily and conveniently replaced after an earthquake at a low cost, which is an important measure to realize recoverable functional cities. Therefore, a new type of friction energy dissipation damper has been designed. First, the components of the damper are described, and the design process, including the base placement area, bolt hole length, and initial slip force, is theoretically analysed. Then, on the basis of a shear wall test, SAP2000 is used to analyse and verify correctness of the model. Furthermore, the dampers are placed in the corner of the shear wall for remodelling. Considering different bolt hole lengths, the hysteretic performance, bearing capacity attenuation, stiffness degradation, and energy dissipation capacity of the model are compared and analysed. The results show that the friction energy dissipation damper can improve the energy dissipation capacity and delay the stiffness degradation and bearing capacity attenuation of the structure. This study provides a theoretical basis for a more detailed engineering design and application.

Interactions between Seismic Safety and Energy Efficiency for Masonry Infill Walls: A Shift of the Paradigm

Currently, the upgrade of existing reinforced concrete (RC) buildings focuses only on energy retrofitting measures due to the current policies promoted in the scope of the European Green Deal. However, the structural deficiencies are not eliminated, leaving the building seriously unsafe despite the investment, particularly in seismic-prone regions. Moreover, the envelopes of existing RC buildings are responsible for their energy efficiency and seismic performance, but these two performance indicators are not usually correlated. They are frequently analyzed independently from each other. Based on this motivation, this research aimed to perform a holistic performance assessment of five different types of masonry infill walls (i.e., two non-strengthened walls, two walls with seismic strengthening, and one wall with energy strengthening). This performance assessment was performed in a three-step procedure: (i) energy performance assessment by analyzing the heat transfer coefficient of each wall type; (ii) seismic performance assessment by analyzing the out-of-plane seismic vulnerability; (iii) cost–benefit performance assessment. Therefore, a global analysis was performed, in which the different performance indicators (structural and energy) were evaluated. In addition, a state-of-the-art review regarding strengthening techniques (independent structural strengthening, independent energy strengthening, and combined structural plus energy strengthening) is provided. From this study, it was observed that the use of the external thermal insulation composite system reduced the heat transfer coefficient by about 77%. However, it reduced the wall strength capacity by about 9%. On the other hand, the use of textile-reinforced mortar improved the strength and deformation capacity by about 50% and 236%, but it did not sufficiently reduce the heat transfer coefficient. There is a need to combine both techniques to simultaneously improve the energy and structural energy performance parameters.

Demystifying the Barriers and Motivators for the Adoption of Base Isolation Systems in New Zealand

A base isolator is a proven system that can significantly reduce any damage to a building in the event of an earthquake. Despite their efficacy, seismic isolators are not widely used in New Zealand, with only about forty systems in use during the 2010 and 2011 Canterbury Earthquakes. This study seeks to investigate why base isolation systems are not frequently used in seismic strengthening projects and buildings in New Zealand. It also focuses on determining ways in which seismic isolators could become more widely used in New Zealand due to increased seismic activity. This study used an exploratory sequential mixed method design, in which qualitative data were collected first through in-depth face-to-face interviews, analysed, and used to construct the quantitative instrument, which was an online questionnaire. Data were obtained from construction professionals such as architects, engineers, site-based construction personnel, and quantity surveyors. The findings of this study indicated the need for an increased awareness of base isolation systems and improved universal guidelines for the design of seismic isolators. The motivators identified include provision of monetary incentives, such as reduced insurance premiums and financial subsidies, to encourage the adoption of seismic isolators. The factors preventing the adoption of base isolation systems in New Zealand were classified as human-related, safety and design-related, and cost-related. The study’s implication is that providing a universal guideline for seismic isolators can enhance designers’ confidence. Likewise, incentives may be provided to property owners to lower the cost of implementing a base isolation system.

A use of natural sisal and jute fiber composites for seismic retrofitting of nonductile rectangular reinforced concrete columns

Given a size of low-rise residential buildings located in seismic-prone areas, it is difficult to rationalize the application of Carbon Fiber Sheet Polymer (CFRP) sheets for the sake of seismic strengthening. Consequently, this study aimed at finding alternate solutions that could justify the cost without compromising on the performance of strengthened buildings. The potential of sisal and jute fibers was investigated in preventing brittle shear failures of short RC columns. A total of 6 RC columns furnishing typical old non-seismic details with a shear span-to-depth ratio of 2.35 were tested in this study. One column served as control whereas one column was strengthened with 2 layers of CFRP sheets. Rest of the 4 columns were strengthened with 2 and 4 layers of sisal and jute fiber composite sheets. Structural performance in terms of failure modes, ductility, energy dissipation, and peak lateral loads was summarized. It was established that both the natural fiber composites could enhance the structural performance of RC columns to a level comparable to that established by CFRP sheets. This too was achieved by reducing the strengthening cost per column relative to CFRP by 35 and 15% for sisal and jute, respectively.

On the Applicability of Conventional Seismic Design Methodologies to Hybrid RC‐Steel Systems

AbstractThis paper analyses the adequacy of the q‐factor approach when applied to hybrid RC‐steel systems. This approach is prescribed by EC8‐1 as the basic design method, and usually referred to as the most conservative. However, due to its simplicity and popularity for the design of new structures, practitioners are more likely to resort to it, than to the more complex nonlinear static and dynamic procedures, when dealing with the seismic assessment and strengthening of existing RC buildings. A case‐study application is thus presented to analyse and discuss the difficulties a practitioner will face when assessing the efficiency of a steel‐brace retrofitting system designed within the framework of EC8‐1.

FRP Tension Ties: State-of-the-Art Review of Existing Design Guidance for Debonding Capacity and Applicability to Concrete Diaphragm Seismic Strengthening

FRP Tension Ties: State-of-the-Art Review of Existing Design Guidance for Debonding Capacity and Applicability to Concrete Diaphragm Seismic Strengthening

Nonlinear numerical parametric study of the number and arrangement of dowels connecting the wall to the bounding frame for the seismic strengthening of RC frames with RC infill walls

Nonlinear numerical parametric study of the number and arrangement of dowels connecting the wall to the bounding frame for the seismic strengthening of RC frames with RC infill walls

Failure modes of reinforced concrete walls under cyclic loading: Experimental study and prediction method

Failure mode identification and prediction of RC walls are of critical importance for seismic strengthening of existing members and target quantification of performance-based seismic design. This paper aims to better understand the failure modes of RC walls under cyclic loading. Firstly, cyclic test was conducted to examine the effect of reinforcement strength (fy = 476 MPa vs 641 MPa), axial load ratio (0.1 vs 0.2), and shear demand to capacity ratio (Vf/vs = 0.38 vs 1.25) on the failure modes of RC walls. Then, the existing experimental data of 168 wall specimens was collected, and the statistical analyses were carried out to obtain the critical parameters for different failure modes, which were used to establish the prediction method for failure modes. Finally, the accuracy of the prediction method was evaluated by the experimental data. The study results show that the larger axial load can both increase the likelihood of concrete crushing as well as various out of plane buckling modes; shear demand to capacity ratio is a critical parameter to affect the failure process and mode of RC walls. The statistical analyses show that when shear span ratio (λ) ≥ 2.7 and Vf/vs ≤ 0.60, the wall specimens fail in flexure; when Vf/vs ≥ 1, or λ ≤ 1.1 and Vf/vs ≥ 0.80, the wall specimens fail in shear, and the wall specimens not within the above ranges fail in flexure-shear mode. The evaluation results show that the prediction method has a reasonable accuracy.

Correction to: Numerical simulation of RC frames infilled with RC walls for seismic strengthening of existing structures

Correction to: Numerical simulation of RC frames infilled with RC walls for seismic strengthening of existing structures

Seismic Strengthening of R/C Buildings Retrofitted by New Window-Type System Using Non-Buckling Slit Dampers Examined via Pseudo-Dynamic Testing and Nonlinear Dynamic Analysis

In the present study, a window-type seismic control system (WSCS) using non-buckling slit dampers (NBSDs) was proposed and developed to address the disadvantages of conventional seismic control systems so that it can be effectively applied to existing reinforced concrete (RC) buildings. Materials testing was also conducted to examine the material performance and energy dissipation capacity of NBSD. A full-scale two-story test frame modeled from existing RC buildings with non-seismic details was subjected to pseudo-dynamic testing. As a result, the effect of NBSD-WSCS, when applied to existing RC frames, was examined and verified, especially as to its seismic retrofitting performance. In addition, based on material testing and pseudo-dynamic test results, a restoring force characteristics model was proposed to implement the nonlinear dynamic analysis of a test building retrofitted with NBSD-WSCS. Based on the proposed restoring force characteristics, nonlinear dynamic analysis was conducted, and the results were compared with those obtained by the pseudo-dynamic tests. Finally, in an attempt to commercialize this NBSD-based WSCS, nonlinear dynamic analysis was conducted on the entire RC building with non-seismic details retrofitted with NBSD-WSCS. The results showed that the RC frame (building) with no reinforcement applied underwent shear failure at seismic intensity of 200 cm/s2, a typical threshold applied in seismic design in Korea. In contrast, in the frame (building) retrofitted with NBSD-WSCS, only minor earthquake damage was expected, and even when the seismic intensity was set to 300 cm/s2, the maximum intensity that had been observed in Korea, only small or moderate seismic damage was expected. These results confirmed the effectiveness of the seismic retrofitting method using NBSD-WSCS developed in the present study.

Numerical simulation of RC frames infilled with RC walls for seismic strengthening of existing structures

Although it is evident that the RC infill wall is an economic and practical way to improve the lateral strength of framed structures and a retrofitting method for existing buildings to withstand earthquake loads, there are still a lot of limitations regarding their application. Codes do not provide any guidance for their design and detailing or specific regulations for their interaction with the bounding frame. Furthermore, specific directions do not exist for the modelling or evaluation of frame bays converted into RC walls, depending on the type and details of the connection. A representation of the real behaviour of the wall and its interaction with the bounding frame during an earthquake is necessary to provide more accurate guiding information. For this aim, numerical models of this structural system were developed and are presented in this paper. The experimental results of the project SERFIN, which was a full-scale four-storey model tested with the pseudo-dynamic method at the ELSA facility of the Joint Research Centre in Ispra, were used to calibrate the numerical models. Two-dimensional (2D) frames were modelled in DIANA FEA, and nonlinear transient analyses were performed to simulate the experimental results obtained from the SERFIN full-scale experiment. In this paper, the FE model simulation of the test specimen is presented along with a comparison between the experimental results and the numerical ones. It was concluded that the developed numerical models capture effectively the behaviour of the studied structural system and can be used for parametric studies to examine the effects of the number of dowels on the behaviour of the system and propose design guidelines based on the results of the parametric study.