Seismic Reinforcement Research Articles

Effect of transverse circular and helical reinforcements on the performance of circular RC column under high explosive loading

Columns are primary load-carrying members of the framed structure which transfer external lateral loads and gravity load of the structure to the foundation. Columns under extreme loadings such as blast may become a local hazard, failure of which can lead to the disproportionate or progressive collapse of the building. Not only the subversive reasons but accidental explosions may also cause the failure of the column(s) or building, resulting in a huge loss of economy and human lives. Blast resistance of the columns in the building is of serious concern under explosive loadings. Following the validation of experimentally tested square RC column with seismic lateral reinforcement carrying axial load subjected to an explosive charge of 100 kg ANFO (82 kg-TNT equivalent) at a scaled distance of 1.00 m/kg1/3 with 10 mm mesh size using ABAQUS/CAE software equipped with concrete damage plasticity model, equivalent circular columns to the experimentally tested one having seismic circular transverse reinforcement, and column with helical transverse reinforcement carrying the same axial load under the blast are considered. Additional transverse reinforcement of CFRP is also considered over confining regions. Additional wrappings of CFRP and mild steel sheets are also used to study their effect on the blast performance of the columns. Blast performance in terms of maximum displacement, stresses, and damage to the columns are compared and discussed. The present research provides insight into the blast performance of the circular RC columns and provisions to reduce the explosive-induced failure risk.

Changes in Seismic Design of Railways, Seismic Reinforcement and Design Examples ①Brief History of Seismic Design for Railway Structures in Japan

Changes in Seismic Design of Railways, Seismic Reinforcement and Design Examples ①Brief History of Seismic Design for Railway Structures in Japan

Performance of axially loaded square RC columns with single/double confinement layer(s) and strengthened with C-FRP wrapping under close-in blast

Very recently a new variant of reinforced concrete (RC) columns confined with a double layer of transverse steel has been introduced by researchers and investigated its performance under axial compression and seismic loading. Analysis of blast performance of such columns is of considerable interest. Most of the columns in a building structure are found to be of square or rectangular cross-section. Being axisymmetric, the circular columns perform better than square/rectangular ones under impulsive loadings. The stability of a structure supported mainly on columns subjected to such loadings depends upon the performance of the columns. Therefore, it is important to enhance the response of supporting RC compression members of square or rectangular cross-sections of a structure subjected to high intense loadings. In this research work, one 3000 mm long, 300 mm × 300 mm square RC column with conventional transverse steel carrying an axial working load of 950kN subjected to 82 kg-TNT-equivalent close-in blast loading at scaled distance 1.0 m/kg1/3 tested experimentally has been first analyzed using the high-fidelity dynamic computer code, ABAQUS/Explicit-v6.15. For comparison, another singly confined concrete column with seismic reinforcement over its entire length is also analyzed. By comparing the numerical results with the experimental results in the open literature, the accuracy of the numerical model is verified. To improve the response, doubly confined RC columns having outer transverse confining steel stirrups of square and inner ones’ diamond/circular geometry with different combinations of stirrup spacing have been considered and investigated. The columns are of the same area of compression steel and carry the same axial load (950kN). Carbon-fiber-reinforced-polymer (C-FRP) wrapping of 2 mm thickness is also considered and modeled using Hashin’s damage initiation criteria and energy-based damage evolution to investigate the blast resistance of the columns. Blast performance in terms of displacement, damage dissipation energy, concrete crushing, and cracking are compared and discussed.

Performance of composite and tubular columns under close-in blast loading: A comparative numerical study

In the present scenario, rapid industrialization and political conflicts across the globe result rise in malicious terrorist activities in the form of blasts and explosions targeting specific civil engineering structures. Damage caused by such blast loading may be of serious consequences in terms of huge material loss and fatalities. Therefore, investigations on construction and strengthening technique to improve the blast resistance of the critical components of the structure are of considerable interest. In the present study, an experimentally tested square RC column with seismic lateral reinforcement carrying axial load subjected to an explosive charge of 100 kg ANFO (82 kg-TNT equivalent) at a scaled distance of 1.00 m/kg1/3 with 10 mm mesh size using ABAQUS/CAE software equipped with concrete damage plasticity model is considered for validation. To have the superior performance of the RC column, efforts have been made by considering eight equivalent RC columns including composite, CFST, CFST with in-plane cross reinforcement, and CFDST to the experimentally tested one under close-in blast are analyzed. The numerical models have been developed by considering equivalent peak pressure of 8.71 MPa under the close-in blast. Parameters such as maximum transverse displacement, stresses, crack depth, and damage to the columns are studied and compared. It has been found that the CFST column with in-plane cross reinforcement and the composite column with seismic reinforcement give superior blast performance under the close-in blast loading. The two superior columns are strengthened with C-FRP wrapping over the mid-height region and analyzed under the same loading. Improved performance of the columns is discussed and compared and the column giving the best performance is identified.

Changes in Seismic Design of Railways, Seismic Reinforcement and Design Examples ②Seismic Reinforcement of Railway Structures with Earthquake

Changes in Seismic Design of Railways, Seismic Reinforcement and Design Examples ②Seismic Reinforcement of Railway Structures with Earthquake

Seismic Permanent Deformation Analysis for Gravel Dams in High Altitude Meizoseismal Areas

It is commonly believed that the permanent deformation is introduced by the meizoseismal impacts of embankment dams, which is impossible to be reinstated and will further endanger the safety and normal use thereof. In this study, a three-dimensional finite element model of the dam have been established with the equivalent nodal force approach to calculate the permanent deformation of the dams under seismic protection. It was indicated by the results that the acceleration response of dams was not intense in the meizoseismal areas and the vertical seismic permanent deformation mainly occurred at the top of the dams, of which the collapse rate is less than 1% with small lateral and horizontal seismic permanent deformation. Moreover, the dam profile has been indicated with inward shrinkage upon the seismic permanent deformation, which is beneficial to the stability of the dam slopes. However, seismic measures are required to improve the seismic performance of the dam area because of the large acceleration and permanent seismic deformation at the dam tops. The research results provide a decision basis for seismic hazard assessment and reinforcement solutions of similar dams.

Nonlinear Seismic Response Based on Different Site Types: Soft Soil and Rock Strata

Site condition is an important part of urban underground space development and construction. The seismic fortification of the site plays an important role in the safety of the whole project. To study the seismic dynamic response of the site under different geological conditions, seismic waves of different intensities (Chichi wave and Kobe wave) were input to a rock site with good geological conditions and a soft soil site, respectively. In this paper, the dynamic responses of these two types of free sites were calculated and analyzed using DEEPSOIL numerical simulation software. The dynamic responses of different types of sites under strong shock and persistent earthquakes are discussed under the equivalent linear and nonlinear conditions, and the related dynamic parameters are studied. The results show that the equivalent linear method is more effective than the nonlinear method, especially in the calculation of the strong nonlinear soft soil response induced by strong earthquakes. The amplification effect is more obvious in rock layer sites under strong earthquakes, and the “weakening” effect of soft soil sites is more obvious. Arias’s strength values show that both types of sites are safe under the incident of the two waves, but soft soil sites have better seismic performance. The results calculated by the equivalent linear method are larger and more unsafe; in particular, in the case of a strong earthquake with a stronger nonlinear Kobe wave, the results are more inaccurate. The purpose of this study is to provide a reference for seismic design and reinforcement measures of underground engineering.

The Seismic Reinforcement Technology of External Cable Stayed Steel Strand on Frame Structure

The Seismic Reinforcement Technology of External Cable Stayed Steel Strand on Frame Structure

Study on the ultimate behavior and the seismic reinforcement method of brace material gusset joint of existing upper road arch bridge

Study on the ultimate behavior and the seismic reinforcement method of brace material gusset joint of existing upper road arch bridge

Study on seismic performance of welding beam reinforced with symmetrical flange plate to H-shaped column after fire

The objective of this paper is to investigate the seismic performance of welding beam strengthened with symmetrical flange plates to H-type column (WBSFPHC) after fire. The accuracy effectiveness of the calculation model was verified using the existing experimental results. Considering the application of practical engineering parameters, the column width-thickness ratio (α), ratio of beam width to column width (β), height-thickness ratio of beam web (γ), width-thickness ratio of stiffener (ε), length thickness ratio of flange plate (η) and temperature (T) were used to perform a parametric study against the post-fire seismic performance of the WBSFPHC connections. Then, 25 calculation models were established to explore hysteretic behavior, stiffness degradation, ductility and energy dissipation capacity of the WBSFPHC connection under post-fire cyclic load. The results showed that the stiffness and bearing capacity of the WBSFPHC connection were improved with the increase of the parameters β and γ, temperature had great effect on the stiffness, stress distribution, energy dissipation capacity and bearing capacity of the WBSFPHC connection. The findings can provide reference and technical support to the seismic performance design, maintenance and reinforcement of such joints after fire.

Seismic behavior of brick cave dwellings: Shake table tests

Brick cave dwellings are a traditional residence widely built and used in the Loess Plateau of China, but the current understanding of their seismic performance is still scarce. In the present study, the weak areas and dynamic response characteristics of brick cave dwellings were explored by performing shake table tests on a 1:4 scaled model. The test results indicate a noticeable increase in the structural model's dynamic response and damage when the PGA (Peak Ground Acceleration) was 0.5 g, while the structural stiffness substantially degraded when the PGA reached 0.6 g. The severely damaged areas on the structural model mainly refer to the piers, middle barrel vault, and Yaolian, and the damage cracks at the wall junctions were denser in particular. Along with the PGA increases, the stiffness degradation of the pier story and roof story was higher than that of the vault story, leading to differences in the dynamic responses between the three stories. Since the flexibility and stiffness degradation of the middle piers were higher than that of the lateral piers, the vertical displacement response of the middle barrel vault constrained by the middle piers was considerably higher than that of the lateral barrel vault. When the chambers opened on the Yaolian of the brick cave dwellings and caused an eccentric distribution in structural stiffness, the dynamic responses of the Yaolian and back wall were rendered differently while a torsion effect was produced. Further analysis also showed that the accumulated hysteresis energy dissipation of each structure story was not the same, the energy dissipation by inelastic deformation increased significantly when the PGA reached 0.6 g, and the structure entered the elastoplastic stage. • The seismic behavior of brick cave dwellings was explored by shaking table tests. • The weak areas of brick cave dwellings under the earthquakes were obtained. • The dynamic characteristics and responses of brick cave dwellings under the earthquakes were explored. • Research results provide support for the seismic design and reinforcement of brick cave dwellings.

Sustainability Perspective to Support Decision Making in Structural Retrofitting of Buildings: A Case Study

The reuse of existing materials in buildings can give a contribution to sustainable practices such as a balance in embodied energy, water, and emission reduction. However, it is not always possible to maintain the existing structural materials because some different technical variables could hamper their usability, namely seismic reinforcement needs, fire safety protection, conservation state, and new legal requirements. The paper follows a case study approach for assessing the technical and environmental performances of structural options for old building retrofitting works. All structural options were analyzed through the results of several categories of environmental impact. Some parameters of a retrofitting management system were also used to frame in a comprehensive way the technical constraints pertaining to building retrofitting works. The structural option choice was taken by the owner with the contribution of the design team and the construction manager of the construction project as well as the results of interviews with other construction professionals, considering the variables related to technical suitability and environmental impact. The results of the study show that the steel structure is the solution that best addresses the technical constraints of the building retrofit works and minimizes environmental impact. The results of the study also suggest that the consideration of other variables other than the technical ones can contribute to the effective functioning of the renovation subsegment of the building market. Some suggestions for further studies to enhance the results of this work are put forward.

Stochastic seismic analysis of geosynthetic-reinforced soil slopes using the probability density evolution method

This paper presents a stochastic seismic analysis of geosynthetic-reinforced soil slopes (GRSS) using the probability density evolution method (PDEM). The combination of the uncertainties of seismic ground motions (SGM), soil properties and reinforcement parameters was considered. The stochastic SGM was generated from a random function based on the spectral representation method. The present method is proved to be more precise than the pseudo-static method and pseudo-dynamic method due to the consideration of the uncertainty of frequency spectrum of seismic excitations, and more efficient than the Monte Carlo simulation method for reducing the number of samples by 39 times. Without involving the stochastic earthquake, the result of the estimated performance would incur large errors since it greatly depends on the selected earthquakes, which may be one of the major reasons for GRSS failure. The slope displacement and the reinforcement strain occur at a relatively narrow region at the beginning, then increase and fluctuate intensively with large uncertainty, and finally become steady in the earthquake decay phase. The reinforcement length has a more substantial influence on the failure probability of the reinforcement than other parameters in the studied ranges. The reinforcement strain increases but the slope displacement decreases with the reinforcement length because of the variation of failure mechanisms.

Collapse Analysis of a Two-Span Reinforced Concrete Bridge Model

The continuous girder bridge is the main type of small- and medium-sized bridges; however, it has poor collapse resistance and suffers frequent earthquake damage. In order to grasp its collapse mechanism and clarify the internal and external factors affecting its collapse resistance, a 1:3-scaled, two-span bridge model subjected to shaking table test research was taken as the research object. The factors such as seismic characteristics, multi-directional seismic coupling, span, pier height, and structural system type were analyzed to determine the influences on the collapse mode of the bridge. The numerical results showed that different ground motion characteristics led to different collapse modes. Vertical ground motion had little effect on the structural response of the bridge. The change of span and pier height significantly changed the collapse resistance. A seismic isolation design could improve the anti-collapse performance, but the collapse mode varied with the system. The final anti-collapse design suggestions could provide reference for the seismic reinforcement of existing continuous girder bridges and the seismic design of continuous girder bridges that will be constructed.

Quantitative analysis of microstructure and mechanical properties of Nb–V microalloyed high-strength seismic reinforcement with different Nb additions

Abstract HRB500E seismic steel bars are mainly used in high-rise buildings near the seismic zone. The influence of different niobium contents (0–0.023%) on the microstructure and mechanical properties of HRB500E seismic reinforcement was studied. Results showed that the grain size of ferrite was between 3.6 and 8.3 μm when only V was added. Meanwhile, as the niobium content increases, the ferrite particles are further refined. After adding niobium, the grain contribution increased by 9%. The addition of niobium significantly refined the grain size of HRB500E seismic reinforcement. The second-phase nano-elliptic precipitate is NbC. The precipitated phase is dispersed on the grain boundary and the matrix, and the dislocation density on the matrix promotes the precipitation of NbC particles along the dislocation line. The second-phase precipitation of niobium can form an effective pinning effect and then refine the pearlite spacing. The microhardness and the tensile strength also significantly improved. The yield strength increased from 509 to 570 MPa.

SEISMIC EVALUATION METHOD BASED ON SEISMIC PERFORMANCE AND ITS APPLICATION FOR EXISTING RC FRAMES

According to statistical analyses and shaking table tests of seismic damage of RC frames, the performance levels and corresponding damage degrees based on inter-story drift subjected to earthquakes were proposed. Seismic vulnerability analysis was adopted to analyze existing RC frame structures built in different historic periods to obtain the vulnerability curves and their matrixes. In order to evaluate the damage degree subjected to the expected earthquake in future, the seismic damage index method was also put forward. Finally, taking an exhibition hall as an example, the seismic performances of the structure before and after seismic strengthening were evaluated, and the effect of seismic reinforcement was verified.

Seismic Performance and Strengthening of Purlin Roof Structures Using a Novel Damping-Limit Device

Purlin roof structure houses, which have the advantages of readily accessible materials and simple construction, are widely used in rural areas of China. However, during earthquakes, the wooden purlins tend to fall off and the walls crack. Therefore, it is necessary to monitor the structural parameters of and strengthen the anti-seismic capacity of these structures. To compensate for the seismic deficiencies of the purlin roof structure, a novel damping-limit device installed at the connection position of the gable and the wooden purlin was proposed. In this study, the seismic performance and reinforcement effect of the brick-wood structure with the purlin roof were analyzed through numerical simulation. The research results indicate that the novel damping-limit device proposed in this study can significantly reduce the local stress concentration and the seismic response of the structure, and thereby rectifying the seismic defect of falling purlin. Moreover, compared with the traditional strengthening method, the novel device is more convenient to install and the reinforcement quality is easier to ensure.

Effect of Blast Loading on Seismically Detailed RC Columns and Buildings

Explosions caused by standoff charges near buildings have drastic effects on the internal and external structural elements which can cause loss of life and fatal injuries in case of failure or collapse of the structural element. Providing structural elements with blast resistance is therefore gaining increasing importance. This paper presents numerical investigation of RC columns with different reinforcement detailing subjected to near-field explosions. Detailed finite element models are made using LS-DYNA software package for several columns having seismic and conventional reinforcement detailing which were previously tested under blast loads. The numerical results show agreement with the published experimental results regarding displacements and damage pattern. Seismic detailing of columns enhances the failure shape of the column and decrease the displacement values compared to columns with conventional reinforcement detailing. Further, the effect of several modeling parameters are studied such as mesh sensitivity analysis, inclusion of air medium and erosion values on the displacements and damage pattern. The results show that decreasing the mesh size, increasing erosion value and inclusion of air region provide results that are very close to experimental results. Additionally, application is made on a slab-column multistory building provided with protective walls having different connection details subjected to blast loads. The results of this study are presented and discussed. Use of a top and bottom floor slab connection of protective RC walls are better than using the full connection at the four sides to the adjacent columns and slabs. This leads to minimizing the distortion and failure of column, and therefore it increases the chance of saving the building from collapse and saving human lives. Doi: 10.28991/cej-2021-03091733 Full Text: PDF

Investigation of seismic behavior of slope reinforced by anchored pile structures using shaking table tests

An anchored pile structure is a type of retaining structure that is widely used in excavation support systems, water-front structures, slope stabilization, and landslide prevention. This structure has good performance because the anchor can limit the displacement and control the deflection of the pile head. Field observations of the performance of various retaining structures during many recent earthquakes have revealed that these structures behave particularly well. However, the dynamic responses and seismic performance of this type of retaining structure in slope stabilization have not been elucidated. In this study, a large-scale shaking table test was conducted to investigate the seismic behavior of a landslide reinforced by anchored pile structures. The acceleration field, anchor force, bending moment, lateral earth pressure along the pile, and permanent displacement of the slope and pile are presented and discussed to systematically determine the seismic responses, reinforcement, and failure mechanism of this retaining structure. The tests results reveal that a landslide reinforced by anchored pile structures achieved good seismic performance even under strong earthquakes. Additionally, some reasonable measures are proposed to improve the seismic performance of a slope reinforced by anchored pile structures. The results obtained by this study can provide a theoretical basis for the seismic performance assessment and design of anchored pile structures.

Seismic Performance and Risk Assessment of Traditional Brick-Wood Rural Buildings Based on Numerical Simulation

The recent earthquakes have caused serious damage to Chinese rural houses. Research on the seismic performance and reinforcement for traditional rural houses is strongly needed. In this study, the seismic performance of traditional brick-wood structural houses in Jiangxi province and surrounding areas is analyzed and confirmed by site investigation and numerical simulation. And, the traditional constructions, such as the purlin roof and the cavity wall, are considered. These construction types can reduce the seismic behavior of rural houses, and limited research has been carried out. This study found that the structure will produce plastic deformation and local damage above 6-degree earthquake fortification action. The damage positions occurred in the walls close to purlins and the walls close to doors and windows. Given the above seismic safety problems, a reinforcement method of reinforced cement mortar strip and mesh surface is proposed, which is suitable for engineering applications for traditional rural houses. The seismic strengthening effect is analyzed by numerical simulation. Comparing the calculation results, it is found that the seismic performance of the structure after reinforcement is significantly enhanced, and the stress concentration of the walls is improved.