Seismic Shear Strength Research Articles

Rapid Urban-Scale Building Collapse Assessment Based on Nonlinear Dynamic Analysis and Earthquake Observations

Rapid damage assessment after an earthquake is crucial for allocating and prioritizing emergency actions. Building damage due to an earthquake depends on the seismic hazard and the building’s strength. While it is now possible to promptly access acceleration data as seismic input through online strong motion networks in urban areas, good models are necessary to evaluate the damage in different zones of the affected area. This study aims to present a rapid method for such an urban-scale building collapse evaluation by conducting a nonlinear dynamic analysis of modeled buildings. Based on the Nagato and Kawase model, this study estimates the yield shear strength of 3-story steel buildings, 3-story reinforced concrete buildings, and 1-story masonry buildings in Sarpol-e-Zahab City after the 2017 Mw7.3 earthquake. The damage ratio is calculated through nonlinear dynamic analyses using estimated records from the main earthquake shock in different city zones. The research found that the seismic yield shear strength of steel and reinforced concrete buildings might be weaker than that of the Iranian seismic code’s standard value. Conversely, masonry-building resistance is stronger than the guidelines assumed. The constructed numerical models can be used for the rapid building damage assessment immediately after a damaging earthquake.

Mechanics guided data-driven model for seismic shear strength of exterior beam-column joints

This study presents an enhanced predictive model for the seismic shear strength of exterior beam-column joints (BCJs). Initially, the principles of strut-and-tie mechanism and variable selection procedures were first utilized to identify the most influential parameters. Subsequently, an evolutionary algorithm, specifically multigene genetic programming (MGGP), was utilized to search for the near-optimal predictive model. The dataset used to develop, train, and test the proposed model was compiled from previously published tests, focusing specifically on cyclically loaded exterior BCJs that encountered shear and flexure -shear failures. The prediction performance of the developed model was assessed through various statistical measures, and then compared with that of other existing models. Additionally, sensitivity analyses were also performed to identify the influence and importance of each design parameter. The results demonstrated that the methodology employed in this study yielded an elegant model that adheres to the underlying mechanics and provides higher prediction accuracy compared to existing models. Furthermore, the sensitivity analyses showed that BCJ shear strength positively correlates with concrete compressive strength, beam reinforcement, joint transverse reinforcement, column intermediate vertical reinforcement, and axial load ratio, while it negatively correlates with the joint aspect ratio. Among these design parameters, beam reinforcement has the greatest influence on the model response, followed by concrete compressive strength. Conversely, column intermediate vertical reinforcement and axial load ratio have the least impact on the model response. The notable prediction capabilities and robustness demonstrated by the developed model render it an efficient design tool with promising potentials for adoption by practicing engineers and for consideration in design guidelines.

Seismic behavior of autoclaved aerated concrete masonry walls reinforced with glass-fiber geogrid

Reinforcing horizontal mortar joints with steel bars can improve the seismic performance of autoclaved aerated concrete (AAC) masonry walls. Nevertheless, the diameter of steel bars can require a large thickness of the mortar joints, which in turn results in the thermal bridging effect. Glass fiber geogrids (GFGs) can be employed to replace steel bars to reduce the thickness of mortar joints, and thus can mitigate the thermal bridging effect. Despite considerable advancements in understanding the mechanical performance of GFGs in masonry walls, their effect on the seismic performance of AAC walls remains unknown. Therefore, this study investigates the effect of different GFG configuration rates on the seismic performance of AAC masonry walls using reciprocating load tests. Furthermore, the effect of different vertical compressive stresses on the seismic performance of GFG-reinforced AAC masonry walls was studied via comprehensive finite element simulations. The test results show that the ultimate load-bearing capacity and ultimate displacements of the wall specimens were enhanced as the GFG configuration rate increased, approaching that of benchmark specimens reinforced with steel bars. On the other hand, the cracking and ultimate loads, along with ultimate displacements of GFG-reinforced AAC masonry walls were significantly improved compared to those of the unreinforced AAC masonry walls. It was also evidenced that the crack formation, failure mode, ductility and energy dissipation capacity of the specimens simulated through the finite element method were highly comparable to that of experimentally tested specimens. Accordingly, the vertical compressive stresses were in the range of 0.1 MPa ∼ 0.6 MPa, while the seismic performance of GFG masonry walls was improved with the increase in vertical pressure. The results of the current study confirm that embedding GFG in horizontal mortar joints can delay the cracking of AAC masonry walls and improve their seismic performance. Ultimately, an empirical equation was developed to calculate the seismic shear strength of GFG-reinforced AAC masonry walls.

Predicting the Influence of Shear on the Seismic Response of Bridge Columns

In the seismic design and evaluation of bridges, a method is required for determining the shear strength of reinforced concrete columns to avoid brittle shear failures. In addition, detailed design and evaluation often require predictions of the complete hysteretic response of bridge columns to accurately model the nonlinear dynamic response of the bridge. Predictions of the shear strength of columns using the provisions of the AASHTO Specifications are compared with the reversed-cyclic loading test results of shear-critical columns. It is found that the Simplified Procedure results in very conservative predictions of the seismic shear strength. The General Procedure provides conservative and more accurate predictions of the seismic shear strength. It is suggested that the AASHTO reduction factor on the concrete contribution resisting shear for low compressive axial load levels be removed. Nonlinear finite element analysis predictions are made for a selection of rectangular and circular columns tested in reversed-cyclic loading and are compared with the experimental results. The ability of nonlinear finite element analysis to predict the reversed-cyclic loading responses of columns with a wide range of variables and having different failure modes is demonstrated.

The evolution of Indonesian seismic and concrete building codes: From the past to the present

The factors primarily affecting the seismic vulnerability of existing concrete buildings are the seismic base shear strength which is regulated in the seismic loading codes and the seismic detailing which is regulated through the concrete design codes since both of them are specified and legally enforceable as the minimum standard. This study provides a comprehensive summary of the evolution of the seismic loading and detailing codes for reinforced concrete buildings in Indonesia from 1970 to the present. It specifically focuses on substantial changes in various Indonesian seismic loading and concrete codes for buildings due to the increase in the seismic demand for both strength and ductility. Moreover, lessons learned obtained from the recent two considerable earthquakes, Palu and Lombok earthquakes 2018, were also presented. The main aim is to construct the universal framework of seismic resistance of existing concrete buildings in Indonesia designed through prior versions of Indonesian codes in line with preparing the first Indonesian National Standard (SNI) for seismic evaluation and rehabilitation. The base shear of the low, medium, and high-rise buildings designed using different versions of Indonesian seismic design codes were also compared comprehensively to indicate their significant changes on buildings and identify the possibility of strength deficiency of existing buildings in several big cities in Indonesia which represent most of the seismic zones.

Near‐Surface Geomechanical Properties and Weathering Characteristics Across a Tectonic and Climatic Gradient in the Central Nepal Himalaya

AbstractShallow bedrock strength controls both landslide hazard and the rate and form of erosion, yet regional patterns in near‐surface mechanical properties are rarely known quantitatively due to the challenge in collecting in situ measurements. Here we present seismic and geomechanical characterizations of the shallow subsurface across the central Himalayan Range in Nepal. By pairing widely distributed 1D shear wave velocity surveys and engineering outcrop descriptions per the Geological Strength Index classification system, we evaluate landscape‐scale patterns in near‐surface mechanical characteristics and their relation to environmental factors known to affect rock strength. We find that shallow bedrock strength is more dependent on the degree of chemical and physical weathering, rather than the mineral and textural differences between the metamorphic lithologies found in the central Himalaya. Furthermore, weathering varies systematically with topography. Bedrock ridge top sites are highly weathered and have S‐wave seismic velocities and shear strength characteristics that are more typical of soils, whereas sites near valley bottoms tend to be less weathered and characterized by high S‐wave velocities and shear strength estimates typical of rock. Weathering on hillslopes is significantly more variable, resulting in S‐wave velocities that range between the ridge and channel endmembers. We speculate that variability in the hillslope environment may be partly explained by the episodic nature of mass wasting, which clears away weathered material where landslide scars are recent. These results underscore the mechanical heterogeneity in the shallow subsurface and highlight the need to account for variable bedrock weathering when estimating strength parameters for regional landslide hazard analysis.

Seismic performance and shear strength of coupling beams using engineered cementitious composites with different reinforcement layouts

The coupling beam is the key component in high-rise coupled-wall and core-tube structures. To further improve the seismic performance and damage tolerance of traditional reinforced concrete coupling beams, engineered cementitious composites (ECC) becomes a prospective choice, due to the superior characteristics including tension strain-hardening and multi-cracking properties. However, there have been only limited researches on ECC coupling beams, causing the lack of comprehensive understanding of the seismic behaviour and practical design formula. In this study, eight large-scale ECC coupling beam specimens with different aspect ratios, transverse and diagonal reinforcement ratios are fabricated and cyclically tested. The seismic performance of coupling beams is thoroughly investigated in terms of the damage and failure modes, energy dissipation, stiffness deterioration, strength degradation and shear distortion. The contribution of ECC, transverse and diagonal reinforcement to the shear strength is evaluated and compared. Besides, the whole-process hysteretic curves of the axial force are reported for the first time. Finally, a shear strength equation is proposed based on the analysis of nineteen specimens collected from the literature and this study. The test results demonstrate that ECC coupling beams with a hybrid reinforcement layout exhibit superior seismic performance, which is a reasonable choice to balance both the seismic and construction performance. It is strongly recommended that axial force should be considered in the strength prediction of coupling beams, with a 10% axial force ratio suggested for design. The proposed method is verified and can give precise prediction for the bearing capacity of ECC coupling beams.

Investigation on seismic performance and shear strength of high‐strength concrete‐filled polyvinyl chloride tube short columns

SummaryThis paper innovatively designs polyvinyl chloride tube (PVCT) with high‐strength concrete (HC) and presents the results of cyclic loading tests on new reinforced high‐strength concrete short columns, including three high‐strength concrete‐filled PVCT (HC‐PVCT) short columns, one high‐strength concrete‐filled steel tube short column and one HC short column. The main objective of this research was to evaluate the seismic behaviors of HC short columns based on the quasistatic test of the columns. The design parameters of the columns in the experiments were axial compression ratio, reinforcement measures, concrete strength, stirrups configuration, and the height‐diameter ratio of tubes. The crack distribution, failure modes, hysteresis loops, skeleton curves, energy dissipation capacity, strength degradation, stiffness degradation, and cumulative damage of the columns were presented and analyzed. The results showed that the HC‐PVCT column had a fuller hysteretic loop and a higher peak load than the HC column. Compared with HC column, the strength degradation of HC‐PVCT columns was slower, and the ductility increased significantly. With a larger axial compression ratio, the ductility of HC‐PVCT columns was decreased. Based on the test and analysis results, a modified HC‐PVCT design method was proposed to calculate the nominal shear strength of HC‐PVCT short columns.

Spectral bearing capacity analysis of strip footings under pseudo-dynamic excitation

ABSTRACT Spectral seismic bearing capacity of strip foundations is evaluated by the limit equilibrium method (LEM). In this study, the pseudo-dynamic approach is followed to take into account seismic accelerations. The formulation of spectral pseudo-dynamic bearing capacity of strip foundations is presented for the Coulomb failure mechanism. The results are reported in the form of joint bearing capacity considering the contributions of cohesion, surcharge, and soil weight, simultaneously. A parametric study is conducted to evaluate the influence of soil friction angle, interface wall friction angle, dimensionless ratio of cohesion, depth factor, primary and shear wavelength values, amplification factor as well as the frequency on the seismic bearing capacity factor. The results of this study are shown in the form of design aids and tabular for the sake of simplicity to be used by engineers. The consistency of the results with those reported in literature shows the ability and efficiency of the methodology presented herein. It is shown that both the seismic loading characteristics and shear strength parameters affect the bearing capacity of shallow footings.

Explicit analytical model for seismic shear strength of RC bridge columns

An explicit analytical model was developed to predict the seismic shear strength of reinforced concrete (RC) bridge columns that failed in different modes including flexure, shear and flexure–shear failure. Shear demand was calculated without iteration based on sectional analysis. The shear capacity was divided into three contributions: the concrete compression zone (CCZ), concrete tension zone, and transverse reinforcements. Rankine's concrete failure criteria were used to determine the contribution of the CCZ, while modified compression field theory was applied to predict the other contributions. The three contributions were found to be dependent on the bottom section curvature based on axial-shear–flexure interaction. Seismic shear strength was obtained with a degraded shear capacity equal to the shear demand. Numerous tests were used to verify the proposed model and to assess the methods proposed in existing codes. Based on the proposed model, an application example and parameter analyses were conducted. The results showed that the proposed model produced better agreement with the test data than the methods of current codes. The contribution of the CCZ dominates RC bridge columns with low transverse reinforcements or high axial load ratios. The influence of the axial load ratio on seismic shear strength can be revealed accurately by the proposed model.

Seismic behavior and shear strength of new-type fired perforated brick walls with high void ratio

A new type of fired perforated brick with void ratio of more than 30% has been developed to improve the applicability of brick masonry structures. When the new perforated bricks are used for load-bearing walls, it will be a question whether the seismic performance of walls could satisfy the requirements under not obviously increasing the cost. This article presents an experimental study to investigate the seismic behavior and shear capacity of new-type perforated brick walls with high void ratio. For this purpose, six cross walls and three longitudinal walls with constructional columns under low reversed cyclic loading were tested, and the failure patterns, hysteretic characteristics, skeleton curves, energy dissipation capacity, ductility and reinforcement strain were observed. The test results indicate that (1) most new-type perforated brick wall specimens display shear failure, and hysteretic curves of cross walls are plump while there is some pinch phenomenon for longitudinal walls; (2) the specimens have considerable deformation and energy dissipation capacity, with displacement ductility factors of over 2.0; (3) the bearing capacity of walls increases but the ductility decreases with an increase of vertical compressive stress, and the bearing capacity and deformation all increase while considering the effect of horizontal reinforcement; and (4) the central brick wall and construction columns could resist shear force together before the peak load, while the shear force would be mainly born by construction columns at the later loading stage. Based on the test results, the constraint coefficient in current Chinese code was modified, and the calculation formula of shear capacity for cross walls was proposed. Comparison of calculated results with test data shows that the method will provide a way to predict the shear capacity of new-type fired perforated brick walls.

How Can Vernacular Construction Techniques Sustain Earthquakes: The Case of the Bhatar Buildings

After the 2005 M7.6 Kashmir earthquake (Pakistan), field observations reported that several buildings manufactured with local traditional techniques resisted well to that strong seismic event. In this paper the attention is focused on a typical vernacular construction technique commonly named as “Bhatar”, still practiced in the Himalayan regions of India and Pakistan. It is grounded upon the lacing or reinforcement masonry concept, i.e. the combination of dry-stacked loose stones with timber beams to increase the wall confinement. Despite its good seismic performances, it has still not been deeply studied from a structural engineering point of view. This paper represents a first attempt to fill this gap. It presents a full analytical study on the structural behaviour of a simple one-storey building unit characterized by a 3.6 m x 3.6 m square plan covered by an heavy wooden roof with 20 cm thick earth coverage, in order to investigate its response under gravity and seismic inertial loadings. Materials properties, static analysis and seismic analysis are discussed. In detail, Shorea Robusta wood and limestone rocks are identified as the most used construction materials for the Bhatar buildings. The Barton's model is applied to characterise the shear strength of the rubble stone layers in the wall. Static analysis reveals that normal stresses at the ground level are around 92 kPa, which can be considered acceptable for common soils. With respect to earthquake, the Bhatar technique can absorb wall cracking and distortion mechanisms, and can dissipate energy through friction between stones. Under the assumption of no vertical ground motion, the acceleration which activates in-plane sliding mechanisms is found to be around 0.5 g, being dependent on the interface friction between adjacent layers. Some preliminary considerations about the out-of-plane seismic behaviour are also provided concerning overturning and bending failure mechanisms. The results are based on assumptions taken by several authors and have not been verified with experimental tests. Nevertheless, some practical suggestions can be derived to improve the seismic shear strength and to ensure friction also in the case of significant vertical component of earthquake ground motions.

Performance of Reinforced Reactive Powder Concrete Beam-Column Joints under Cyclic Loads

An experimental research was carried out to investigate the seismic performance and shear strength of reactive powder concrete interior beam-column joints subjected to reverse cyclic loads. Four beam-column joint specimens were cast and tested in the investigation. The failure characteristics, deformational properties, ductility, and energy dissipation of reinforced reactive powder concrete interior beam-column joints were analyzed in this paper. The shear strength of joints was calculated according to the GB5001-2010 and ACI 318-14. The results shows that reactive powder concrete beam-column joints have a higher shear-cracking strength and shear carrying capacity and strength degradation and rigidity degradation are not notable. Additionally, the use of RPC for beam-column joints can reduce the congestion of stirrups in joints core. The shear force in the RPC joint is mainly carried by the diagonal strut mechanism; the design expression of ACI 318-14 can be used for calculating the shear strength of RPC joints, which has a safety margin of 22%∼38% in this test.

Cyclic loading tests and shear strength of steel reinforced recycled concrete beam–column inner joints

SummaryTo study the seismic behavior and shear strength of steel reinforced recycled concrete (SRRC) beam–column inner joints, four 1:2.5 scaled specimens with different replacement percentage of recycled coarse aggregates were fabricated and tested under cyclic lateral loadings. The failure modes of SRRC joints were observed, and the various mechanical indexes of SRRC joints, including hysteresis loops, envelope curves, load carrying capacity, ductility, energy dissipation capacity, and stiffness degradation, were analyzed. The results indicate that the main failure mode of the SRRC joints is the shearing diagonal compression in the core zone of joint. The seismic behavior of the SRRC inner joints degrade only slightly compared with the ordinary steel reinforced concrete inner joints. Based on the test and analysis results, a modified design method is proposed to calculate the nominal shear strength of SRRC inner joints.

Prediction for potential landslide zones using seismic amplitude in Liwan gas field, northern South China Sea

The Liwan (Lw) gas field located in the northern slope of the South China Sea (SCS) is extremely complex for its sea-floor topograghy, which is a huge challenge for the safety of subsea facilities. It is economically impractical to obtain parameters for risk assessment of slope stability through a large amount of sampling over the whole field. The linkage between soil shear strength and seabed peak amplitude derived from 2D/3D seismic data is helpful for understanding the regional slope-instability risk. In this paper, the relationships among seabed peak, acoustic impedance and shear strength of shallow soil in the study area were discussed based on statistical analysis results. We obtained a similar relationship to that obtained in other deep-water areas. There is a positive correlation between seabed peak amplitude and acoustic impedance and an exponential relationship between acoustic impedance and shear strength of sediment. The acoustic impedance is the key factor linking the seismic amplitude and shear strength. Infinite slope stability analysis results indicate the areas have a high potential of shallow landslide on slopes exceeding 15° when the thickness of loose sediments exceeds 8 m in the Lw gas field. Our prediction shows that they are mainly located in the heads and walls of submarine canyons.

Research on seismic behavior and shear strength of SRHC frame columns

The seismic behavior of steel reinforced high strength and high performance concrete (SRHC) frame columns was investigated through pseudo-static experiments of 16 frame columns with various shear span ratios, axial compression ratios, concrete strengths, steel ratios and stirrup ratios. Three kinds of failure mechanisms are presented and the characteristics of experimental hysteretic curves and skeleton curves with different design parameters are discussed. The columns’ ductility and energy dissipation were quantitatively evaluated based on seismic resistance. The research results indicate that SRHC frame columns can withstand extreme bearing capacity, but the abilities of ductility and energy dissipation are inferior because of SRHC’s natural brittleness. As a result, the axial load ratio should be restricted and some construction measures adopted, such as increasing the stirrup ratio. This research established effect factors on the bearing capacity of SPHC columns. Finally, an algorithm for obtaining ultimate bearing capacity using the flexural failure mode is established based on a modified plane-section assumption. The authors also established equations to determine shearing baroclinic failure and shear bond failure based on the accumulation of the axial load force distribution ratio. The calculated results of shear bearing capacity for different failure modes were in good agreement with the experimental results.

Shear capacity of steel fibre reinforced concrete coupling beams using conventional reinforcements

The seismic performance of coupled shear wall systems is governed by the shear resistance of their coupling beams. Steel fibre reinforced concrete (SFRC) is widely applied in coupling beams for its positive contribution to their ductility. This study deals with the seismic behaviour of SFRC coupling beams using conventional reinforcements and develops a simplified model that applies the Mohr-coulomb failure criterion to predict the seismic shear strength of SFRC coupling beams. Variables studied include concrete compressive strength, fibre volume fraction and span-to-depth ratio. Results show that steel fibres improve the shear strength, deformation and energy dissipation capacity of the SFRC coupling beams. When fibre volume fraction is greater than 2.5% or span-to-depth ratio excesses 2.5, SFRC coupling beams present an excellent seismic performance and avoid effectively brittle shear failure. Using the Mohr-Coulomb failure criterion, a simplified shear model was proposed for SFRC coupling beams and presents a good accuracy and reliability. Furthermore, taking into account the negative effect of span-to-depth ratio, the proposed shear model was modified further. The comparative results demonstrated that the new shear model presents a more reasonable assessment accuracy and higher reliability.

Proposal of a complete seismic shear strength model for circular concrete columns

A complete shear strength model is proposed to define the relationship between seismic shear strength and lateral drift ratio of circular concrete columns. The proposed bi-linear model comprises the initial shear strength branch and the shear strength degradation branch, and it can trace the degradation of shear strength along with lateral deformation. The formula to assess the initial shear strength is derived from the equilibrium of the forces acting on the primary shear failure plane and Mohr–Coulomb failure criteria for concrete, while the degradation slope of shear strength is associated with a factor indirectly representing the contribution by the so-called dowel action of longitudinal reinforcements. Another feature of the proposed model is that it can be used to directly calculate the seismic shear strength of circular columns without transforming circular section into an equivalent rectangular or square section. In order to calibrate the proposed model and verify its reliability and accuracy, eighty-eight relatively large scale circular concrete columns that many researchers have reported failing in shear are collected. These previous tests cover a wide range of structural factors such as concrete strength, axial load ratio, yield strength and amount of transverse as well as longitudinal reinforcements, and shear span ratio. Comparisons between the experimental results and the calculated ones indicate that the proposed model can predict the seismic shear strength and trace the shear strength degradation till large deformation more accurately than previous models.

Research of Masonry Shear Strength under Shear-Compression Action

The failure criteria and calculating methods of static and seismic shear strength of masonry under combined shear-compression action have been researched in this paper. According to the least energy consumption principle and the failure criteria of orthogonal anisotropic materials, the correlated formulae of masonry under combined shear-compression action are established. The correlated formulae are in good agreement with experimental results. On this basis, the calculation formulae of the static and seismic shear strength are established. The calculation formulae uniformly use the axial compression ratio as main variable to express. By analyzing examples, it shows that calculations by formulae given in this paper are in accordance with values of "Code for design of masonry structures" (GB 50003-2011) and "Code for seismic design of buildings" (GB 50011-2010). The methods in this paper may provide important references to engineering design as well as code revision.

Seismic shear strength and deformation of RC columns failed in flexural shear

This paper investigates the seismic shear strength and deformation capacity of flexural shear critical columns in the post-yield range of longitudinal reinforcement. In total, 24 reinforced concrete (RC) column specimens with span-to-depth ratios ranging from 1·63 to 6·16 and volumetric ratios of transverse reinforcement of 0·77% and 1·54% were tested under constant axial load ratios of 0·2 and 0·5 and cyclically reversed horizontal load. Of these 24 RC column specimens, seven failed in flexure, two failed in shear and 15 failed in flexural shear. Based on the test results, simple models are proposed to predict the shear strength and displacement capacity of columns failed in flexural shear mode. The proposed shear model includes the effects of span-to-depth ratio, axial load ratio, transverse reinforcement and displacement ductility. Analytical results from the proposed model were compared with test data and consistent agreement was achieved.