Abstract:Resilience, as a new concept in disaster risk management, has become a research hotspot in the field of disaster prevention and mitigation. Considering the significant role of the healthcare system in urban operations and post-disaster rescue, regional medical systems should possess sufficient resilience and provide continuous medical services during and after earthquakes. How to comprehensively consider the safety of multiple hospitals and transportation systems within a region, their emergency response capabilities, integration, and collaboration of multiple systems, effectively assess the seismic resilience level of post-earthquake regional medical systems, and propose scientific improvement suggestions, hold important theoretical significance for the construction of resilient urban and rural areas. This paper, through reviewing domestic and international literature, elucidates the concept and connotation of regional medical system resilience, summarizes the key points of resilience assessment in the two phases of short-term emergency and long-term restoration after earthquakes, and generalizes the existing assessment framework for regional medical system resilience. It elaborates on existing assessment methods from four aspects: hospital cluster system, medical-oriented transportation system, emergency medical service system, and interdependent transportation-healthcare system. The research on regional medical system resilience aims to enhance its resistance, short-term adaptability, and long-term recovery when facing disasters. These studies are of great significance for meeting both emergency and daily medical needs and guiding post-disaster recovery. While some progress has been made in the research on seismic resilience of regional medical systems, there are still some challenges. The paper concludes with an outlook on potential directions for future research.

Abstract:To achieve highly durable resilient structures, a novel composite column was devised. This column utilized steelFRP composite bar (SFCB) as an alternative to steel reinforcement, along with the incorporation of engineered cementitious composites (ECC) instead of normal concrete within the plastic hinge region. Quasi-static tests of SFCBECCconcrete composite columns were conducted under an axial load ratio of 0.13. The influence of FRP content in SFCB (0%, 43.6%, 100%) and the matrix type in the plastic hinge region (ECC, concrete) on the seismic behavior and resilience of the composite columns was assessed. Subsequently, parameter analyses were conducted through OpenSees, exploring the effect of axial load ratios, SFCB reinforcement ratios and ECC strengths. The research showed that the utilization of SFCB endowed the specimen with post-yield stiffness property, facilitating the swift restoration of its original functionalities without repair until a 2% drift ratio. The residual deformation of the composite column decreased with the increasing FRP content in SFCB, but its initial stiffness and peak bearing capacity correspondingly declined. Substituting ECC for normal concrete in the plastic hinge region can further mitigate residual deformation, coupled with a remarkable increase in both peak bearing capacity and ductility. The parameter analyses revealed that increasing the axial load ratio enhanced the bearing capacity of the SFCBECCconcrete composite column, but reduced ductility. Moreover, as the reinforcement ratio of SFCB and the strength of ECC increased, the bearing capacity and ductility correspondingly were amplified. In practical engineering applications, it is possible to rationally design the material properties of SFCB and ECC to meet the specific requirements for structural stiffness, strength, and reparability.

Abstract:To meet the needs of earthquake losses and structural seismic resilience evaluation, it is key to establish the seismic fragility functions. A database containing 227 SRC columns under repeated cyclic loads is established based on the existed experiments in this study. All the SRC columns satisfy the requirements of the Chinese ‘code for design of composite structures’(JGJ 138—2016). Considering the difference in failure model, the components are divided into ductile SRC columns and brittle SRC columns. The damage state classification criteria and corresponding repair methods for different groups are given. Then, the drift is taken as the engineering demand parameter (EDP), the drift limits of each column corresponding to different damage states are extracted based on the hysteresis information. After that, the fragility functions of SRC columns under different groups and damage states are developed using FEMA P-58 method. Finally, the table of fragility function parameters that compatible with the ‘standard for seismic resilience assessment of buildings’(GB/T 38591—2020) is given. The effects of seismic grade and axial load ratio on the fragility function parameters and fragility curve of SRC columns are compared. The role of the proposed fragility function in seismic resilience evaluation is demonstrated, by analyzing the seismic resilience of an SRC frame structure office building.

Abstract:As key components in urban transportation network, bridges play crucial roles in post-earthquake relief and reconstruction efforts. However, existing studies on post-earthquake losses of urban bridges primarily concentrate on repair costs for structural damage, paying less attention to the loss of vehicular traffic capacity, which makes it difficult to provide effective guidance for post-earthquake emergency responses and bridge rehabilitation decisions. Therefore, in this paper a method was proposed to assess the loss of post-earthquake traffic capacity of a bridge by comprehensively considering the seismic damage to bridge components and its impact on vehicular traffic. Firstly, in order to accurately analyze the effect of the earthquake on the bridge structure system, a seismic fragility analysis of the bridge system was conducted using the copula function, considering the interdependence of damage to bridge components. Secondly, an evaluation method was proposed for estimating the loss of traffic capacity in bridges due to earthquakes. Finally, the proposed method for assessing post-earthquake vehicular traffic capacity loss of urban bridges was tested through an example of a 4-span continuous girder bridge, which proves that it is more accurate and has less dispersion and uncertainty compared to existing assessment methods. Compared to traditional qualitative and subjective postearthquake functionality assessment of the damaged bridge, the proposed analytical approach considers the specific impact of seismic damage to bridge components on the traffic capacity of the bridge from a physical perspective, and offers a mathematical model for the decision-making process.

Abstract:To investigate the non-Gaussian features of fluctuating wind pressures on rectangular high-rise buildings with large side ratios, wind tunnel tests were conducted on scale models with side ratios ranging from 1/9 to 9. Based on the results, the third and fourth statistical moments of wind pressures on building surface were analyzed. Zones of Gaussian and non-Gaussian were classified for rectangular buildings with various side ratios. The relationship between spatial correlation coefficient of wind pressure and non-Gaussian intensity was studied and a new method for estimating the mean reattachment length at building side wall was proposed by evaluating the correlation coefficient of wind pressure. The results show that on the side wall, the non-Gaussian wind pressures are related to the distance from the leading edge. Apart from the non-Gaussianity in the corner of windward wall, separated flow regions of side wall and leeward wall noted by some literature, wind pressures behind the area where reattachment happens present non-Gaussian nature as well. The correlation coefficient method proposed in this paper has good accuracy in calculating the mean reattachment length, and the mean reattachment length calculated by the correlation coefficient method along the height changes in a parabolic shape.

Abstract:To enhance the service and mechanical performance of hollow reinforced concrete (HRC), this study introduces a novel composite column, named concrete-filled double-skin corrugated steel tube (CFDCST). This paper conducted a total of 4 large-size CFDCST short columns and 2 HRC short columns, and the main parameters of the test were the type of specimen and the type of outer corrugated steel tube (CST). The failure modes were analyzed and the key mechanical indicators such as the load-bearing capacity, peak strain, and ductility coefficient of the specimens under different parameters were compared and analyzed. The load-CST strain curves were obtained to reveal the confinement mechanism and verify the influence of the outer CST types. The results show that the outer CST can provide confinement to the sandwiched concrete and the smaller the helical angle, the larger the confinement effect. The inner CST primarily offers effective support for unconfined inner concrete wall to preserve the integrity of the cross-section. When the nominal confinement factor and the hollow ratio were basically similar, due to the slippage of the lock-seam, the peak stress, peak strain, and ductility coefficient of CFDCST columns with large helical angle were 15.5%, 21.8% and 16.7% lower than those of CFDCST columns with small helical angle, respectively. When the total steel ratio was basically similar, the load-bearing capacity, peak strain, and ductility coefficient of the CFDCST columns with small helical angle were 10.6%, 36.2% and 50.0% higher than those of HRC columns. Finally, based on the test results, the applicability of 3 typical bearing-capacity formulas was assessed and the corresponding design recommendations were given subsequently.

Abstract:For slab-column connections subjected to vertical loads and unbalanced bending moments, the unbalanced bending moment is typically equated to vertical loads in most existing methods for calculating their punching capacity. However, there is significant controversy regarding the calculation of the unbalanced bending moment ratio coefficient in existing methods, and the coupling effect between vertical loads and unbalanced bending moments has not been adequately considered. Therefore, this paper first proposes a new equation for calculating the punching capacity of slab-column connections under vertical loads only and validates it through comparison with experimental results. Additionally, a novel equation for calculating the flexural capacity of slabs under unbalanced bending moments is proposed. Based on experimental results and considering the bending-shear correlation, an equation for calculating the punching capacity of slab-column connections under the combined action of vertical loads and unbalanced bending moments is then derived. Finally, the proposed method is compared with various design code methods. The results indicate that the proposed method can more accurately predict the punching capacity of slab-column connections.

Abstract:The study investigates the bearing capacity of specially shaped, concrete-filled steel tube columns, emphasizing the impact of reentrant corners. A novel design was proposed, involving the welding of one cold-formed, thin-walled square steel tube and two U-shaped steel tubes into an L-shaped configuration, which is then filled with concrete to form an L-shaped concrete-filled cold-formed thin-walled steel tubular columns. To explore this concept, a series of axial load tests were conducted on 10 specimens with total of 5 groups. These experiments were complemented by finite element analysis to assess the effects of various parameters, including steel tube thickness, protrusion length of the U-shaped tubes, and steel material strength, on the structural integrity and ductility of the columns. Results indicate that the predominant failure mechanism involved localized buckling in the upper-middle region. An increase in the U-shaped tubes protrusion length was found to enhance structural capacity up to a certain threshold, beyond which flexural-torsional failure becomes prevalent. Additionally, both the structural capacity and ductility of the columns were positively correlated with increases in steel tube thickness and material strength. The strength of the concrete was observed to have a minimal impact on the initial stiffness and peak load of the columns, yet significantly influenced the descending phase of the load-deflection curve. Moreover, concrete stresses were more pronounced at the reentrant corners of the specimen ends and mid-sections compared to the lateral mid-sections, suggesting an enhanced restraint by the combination of U-shaped and rectangular steel tubes in these regions. According to the“unified theory”, two sets of calculation formulas for loadbearing capacity were proposed. These formulas not only align closely with experimental results but also demonstrate robust applicability across a wide range of constraint effect coefficients, from 0.44 to 1.94.

Abstract:Modular technology is driving innovation in the design and development of the next generation of nuclear power plants. Steel-plate concrete (SC) structure, characterized by their exceptional working performance and industrial construction efficiency, hold broad application prospects in modular structures. The SC wall-RC slab connection joint serves as a pivotal force transmission element between the SC module structure and the RC structure. and its connection joint design must ensure effective load-transfer performance and the modular construction feasibility. To investigate the shear performance of SC wall-RC slab connection joints, cyclic loading tests were conducted on two ‘thin-wall thick-slab type’ specimens employing different connection methods including rebar-coupler connection and additional shear keys as per GB/T 51340—2018 recommendations. All specimens suffered flexural and shear failure of the RC slab, with the primary failure path being from the loading end to the root of the RC slab. Remarkably, even without shear keys, the connection surfaces met shear resistance requirements. During testing, the straight-threaded rebar sleeves showed no signs of slipping, and neither the rebars nor the weld seams failed. Furthermore, the joint exhibited high ductility coefficients exceeding 4, indicating excellent load transfer behavior for the rebar-coupler connection. This suggests that the rebar-coupler connection can effectively serve as a connection method for SC wall-RC slab joints. However, the core region of the joint was identified as a shear weak zone. To meet full-strength connection design criteria, the volumetric steel ratio of tie-bars in the core region should not fall below 0.59%.

Abstract:To study the quantitative influence and action mechanism of structural size and fiber volume fraction on the splitting tensile strength of basalt fiber reinforced concrete (BFRC) at extreme low temperature, four sizes (side lengths of 0,0, 150, and 200 mm) and four fiber volume fractions (fraction range of 0%~0.5%) of BFRC cubic specimens were designed for static splitting tensile failure tests at room and low temperatures (temperature range of 20~-90 ℃). The experimental results show that all the splitting tensile strengths of different type of concrete increase linearly with the decreasing temperature (with a maximum increase of nearly 130%), showing a significant low-temperature strengthening effect. The incorporation of basalt fibers can slightly improve the low-temperature strengthening effect of splitting tensile strength. All the splitting tensile strengths of BFRC with different fiber volume fractions show a certain fiber reinforcement effect, which can be enhanced with the increase of volume fraction. At extreme low temperature, the dominant failure mode of basalt fiber changes from pull-out failure to rupture failure, which can cause the enhancement of fiber reinforcement effect with the decreasing temperature. The size effect on splitting tensile strength increases with the decreasing temperature, while the addition of basalt fibers can effectively weaken the size effect (with maximum weakening degree of 25.8%). This study provides an effective reference for the applications of BFRC in engineering structures exposed to extreme low-temperature environments.

Abstract:The traditional grouting sleeve manufacturing process is hindered by its complexity, high raw material costs, and challenges in ensuring grouting quality, which has restricted the widespread adoption of prefabricated assembly buildings in China. To address these issues and promote economical, environmentally friendly, and efficient development in the construction industry, an innovative steel grouting sleeve connection technology was developed. This new approach employs a “rolled spiral rib grouting sleeve” in combination with “Bingham-like fluid grout,” which creates a more secure mechanical interlock between the reinforcement bar and grout, as well as between the grout and sleeve. This enhanced interlocking mechanism significantly improves the load-bearing capacity of connected components. The developed technology offers several advantages, including costs reduced, construction processes simplified, and grouting quality assurance improved. To determine the minimum anchorage length of reinforcement bars within this connection system and to compare the connection performance between centered and offset butt joints, unidirectional tensile tests on 34 joint specimens were conducted, and the damage modes and various structural performance indices of the specimens were thoroughly analyzed. The results indicate that the differences in connection performance is minimal between offset and centered butt joints within the sleeve. Additionally, the internal convex ribs within the rolled sleeve significantly enhance grout slip resistance and provide sufficient bond anchorage to meet connection performance requirements. Preliminary findings suggest that the minimum anchorage length of the reinforcement in this proposed connection system can be as short as 10 times the diameter of the reinforcement for offset butt joints.

Abstract:To enhance the process and performance of precast concrete component rebar connections, a grout-anchored rebar butt connection was proposed. Uniaxial tensile tests were conducted on the new type of rebar connection specimens, to assess the reliability of force transmission, considering variations in rebar diameter, concrete strength, and grouted length. The experimental results indicated that the tensile performance of the grout-anchored rebar butt connection was governed by both the grouted length of the rebar and the load-bearing capacity of the splice bars, with no significant correlation to the concrete strength. Under identical splice rebar configurations, specimens with 12 mm and 14 mm diameter rebars fractured with grouted lengths of 0.5la(basic anchorage length of the tensile steel bar) and 0.6la, respectively, while those with 16 mm diameter rebars fractured at grouted lengths of 0.6la. By data analysis suggested that the grouted length for connecting rebars with diameters ranging from 12 to 16 mm should be controlled to the value of 0.6la. Under the condition that the splice rebars and the connecting rebars are of the same grade, the splice rebars for 12~14 mm connecting rebars should be designed as 4C8, and those for 16 mm diameter connecting rebars as 6C8. Additionally, the rebar heading structure could ensure full anchorage of the rebars, and its specific dimensions could guide the rebar processing. The spiral reinforcement has no significant effect on the tensile performance of the rebar connection and can be designed with reference to the parameters of this test.

Abstract:To study the effects of lap length and rebar diameter on the mechanical properties of typeⅡAPC connector, 63 specimens were subjected to uniaxial tensile test, and the failure mode, ultimate bearing capacity, ductility, and bond stress of the connector were analyzed. Test results showed that with the same diameter of rebars, as the lap length increased, the average bond stress decreased, and the strength, ductility, and total elongation at maximum force of the specimen had significantly increased. The residual deformation had decreased overall. The strength, ductility, total elongation at maximum force, and residual deformation of the specimen with tensile failure of rebars met the requirements of the specifications. During the loading process, the short side longitudinal and long side circumferential directions of the middle section of the sleeve were always under tension. Under ultimate load, as the lap length increased, the circumferential compressive strain on the short side of the middle section of the sleeve first transformed into tensile strain and then developed towards compressive strain, and the longitudinal compressive strain on the long side transformed into tensile strain. When the relative lap length was the same, the ultimate bearing capacity increased with the rebar diameter increased. The proposed formulas for calculating the ultimate bond strength and critical lap length are in good agreement with experimental values, and provide references for practical engineering applications. Under uniaxial tension, when the diameter of the rebar is not greater than 18 mm, it is recommended that the connector lap length should be greater than 12d.

Abstract:To accurately analyze the shrinkage behavior and mechanism of cement-based materials containing calcium sulfoaluminate expansive agent under drying conditions and reveal the mechanism of the decline in the compensatory shrinkage effect of calcium sulfoaluminate expansive agent under low relative humidity conditions, the non-destructive low-field nuclear magnetic resonance relaxation technique was adopted to monitor the development of drying shrinkage of white cement paste with and without calcium sulfoaluminate expansive agent at different levels of relative humidity for 10 months, as well as X-ray diffraction test, mass and length monitoring for specimens. From the perspective of both water content and its state, the evolution of drying shrinkage of white cement paste was quantitatively described, the relationship between drying shrinkage and relative water loss was established, and the mechanism of CSA increasing drying shrinkage was elucidated. Results indicate that, dry in environments with 75%, 43% and 11% RH, water loss and drying shrinkage of white cement paste continually increase until stabilization. The relationship between drying shrinkage and relative water loss of specimens in the three types of environments remained almost the same.With the extension of drying time, the drying shrinkage caused by unit water loss initially decreases and then increases. This change can be explained by the difference of water loss in pore at all levels in cement paste during the drying process, and the non-identical mechanism of drying shrinkage under different humidity conditions. When calcium sulfoaluminate expansive agent is mixed into cement-based materials, C-S-H gel nanopore structure will be coarsened to some extent, easy to lose more evaporable water when drying, and ettringite generated by the hydration of the expansion agent will also lose 2 to 5 water of crystallization, both of which together lead to the net slurry moisture loss and drying contraction are increased. In the application of calcium sulfoaluminate expansive agent in the low humidity environment, it needs to pay attention to these two factors leading to the contraction of the impact of increased fall.

Abstract:In order to investigate the effect of the stiffening structure on the failure mechanism and bearing capacity of the N-type joint, static loading tests under axial compression on brace were performed on strengthened joints and basic joint. The test results show that the failure mode of the basic joint is the buckling of the upper flange of chord, while the failure mode of the reinforced joints are the buckling of the stiffened ribs and the cracking of the weld between cover plate and flange of chord. The bearing capacity of the strengthened joint increases by 9.4%~36.5% compared with that of the basic joint. Increasing the thickness of the cover plate can obviously improve the bearing capacity of the gap N-joint. The finite element parameter study of the gap N-joints of Q460C steel square tube reinforced by clover plate and stiffening ribs was carried out by using ABAQUS software. The effects of the ratio of width to thickness of chords, γ, the ratio of the thickness of chord to brace, η, the ratio of the width of chord to brace, β, the angle between tensile brace and chord, θ, the ratio of the gap between two braces to the width of chord, ξ, on failure mode of gap N-joints, stress distribution, load-displacement curve of chord and fracture index, I_f of fillet weld between cover plate and chord flange were investigated. Based on the results of experiment and numerical simulation, the formula of bearing capacity calculation for the gap N-joints of Q460C steel square tube strengthened with cover plate and stiffening ribs was derived and the structural design suggestions were put forward.

Abstract:The efficient conversion between building information modeling (BIM) and structural analysis models in steel structures is required. The expression method of the industry foundation classes (IFC) standard was analyzed in this paper and a BIM-based model conversion algorithm for steel structures was developed and applied to the ABAQUS analysis platform. The algorithm can extract the information of structural members, adjust their spatial location, and automatically add analysis data. Based on C# language and the Xbim toolkit, a software was developed and verified by a steel frame, and then applied to the model conversion and structural analysis of Anyang Tourist Transport Center. The results demonstrate that the developed algorithm and software can accurately convert the structural data of steel structures from the design BIM models to the structural analysis models of ABAQUS. Compared to the traditional approach of directly establishing structural analysis models in ABAQUS system, the proposed algorithm can significantly improve the efficiency of structural modeling and analysis for complex structures.