PROBABILISTIC RELIABILITY ANALYSIS OF A BENDING CLT ROOF SLAB BASED ON DEFLECTION CRITERION

Experimental Investigations and Probabilistic Risk Assessment of Failure in Masonry Buildings with Load-Bearing Walls

The aim of this study is to determine the reliability level (the probability of failure-free operation) of a masonry building with load-bearing walls based on the conducted experimental investigations. The objective of the study is to compare the obtained reliability and failure risk values with the corresponding values calculated using the results of the structural certification. In 2017–2018, and subsequently in 2023–2024, a comprehensive structural certification of the multi-apartment residential building stock was carried out for the first time in the city of Almaty. A total of 1609 multi-story masonry buildings with heights of two to four stories were identified. Based on the certification results, quantitative estimates of the prior and posterior probabilities of failure and reliability for masonry buildings were obtained for the first time. The recurrence of earthquakes was taken into account. The novelty of the study lies in the experimental investigation of a three-story masonry building of series 308. The dynamic excitation was generated by an inertial vibration machine installed on the floor slab. As the inertial load increased, the resonant vibration period changed by a factor of three. This indicates that the building underwent significantly nonlinear deformation. The structure sustained substantial damage. Using statistical simulation methods based on the experimental data, the prior probabilities of failure for masonry buildings were calculated. In this case, the seismic action was modeled as a non-stationary random process with the deterministic envelope proposed by F. F. Aptikaev. Probabilistic estimates of the reliability of masonry buildings were obtained from the certification results both with and without taking into account the recurrence of earthquakes. The obtained estimates of reliability and failure probability can be used to develop practical recommendations aimed at reducing risk and expected losses in the event of possible earthquakes. It is recommended that masonry buildings with load-bearing brick walls either be structurally strengthened or be demolished.

PROBABILISTIC STRUCTURAL ANALYSIS

Optimal Design of Geometrically Nonlinear Steel Structures Using Advanced Analysis

Advanced analysis has been shown to improve material efficiency in statically indeterminate steel-framed structures compared with member-based linear elastic design methods. However, limited research has investigated its applicability to geometrically nonlinear steel structures where residual stresses are induced by the bending process. In this study, the material optimization potential of advanced analysis has been quantified for two arch-based structures by comparing the volume of steel required to satisfy the criteria of both the system and member-based analysis methods in accordance with AS 4100:2020. The two structures were analyzed using the finite element analysis software Strand7 (R3.1.6) and subjected to combined gravity and wind loading in alignment with the serviceability and ultimate limit states specified in AS 1170.0:2002. System behavior was analyzed through the Arc-length plastic zone method. The results indicate that in one of the arch-based structures, advanced analysis can improve material utilization by 8.1%. Provided that future research both validates the use of the reduced stiffness method for treatment of initial geometric imperfections and verifies system reliability factors for structures with curved geometries, advanced analysis presents a practical design method for this structure. Comparison of the two case studies found that advanced analysis has the potential to improve material efficiency only when linear elastic failure is governed by ultimate limit state criteria. It is therefore evident that the material optimization findings of this research cannot be generalized to all arch-based structures, as they are contingent upon the geometry of the model analyzed, the loading scenarios considered, and the deflection limits adopted.

Justification of the technical condition boundaries of structures based on the limit state method

This article examines the theoretical prerequisites for establishing quantitative limits for the technical condition of reinforced concrete structures (limited serviceability and emergency), expressed as fractions of the design bearing capacity. It is noted that current regulatory documents, including GOST 31937, lack direct recommendations on the permissible reduction in bearing capacity due to defects. The results of a summary of experimental data are presented, confirming the presence of a safety margin of up to 30% and a deformability margin of up to 50%, provided that regulatory design requirements are met. An analytical justification for the technical condition limits is provided based on a comparison of the calculated bending moment according to SP 63.13330 and the ultimate actual moment achieved with full realization of the curvilinear stress diagram in the compressed zone of concrete. A ratio in the range of 0.7–0.77 was obtained for a rectangular diagram and 0.55–0.77 for a triangular diagram. An analysis is provided of the reserves incorporated in the reliability factors for materials, operating conditions, and responsibility, as well as the performance characteristics of bending reinforced concrete elements in the ultimate limit state. Practical limit values were proposed: 0.9 for a limited serviceability condition (a 10% reduction in bearing capacity from the design value); and 0.75 for an emergency condition (a 25% reduction), which is consistent with the analysis of experimental and theoretical data.

Seismic Assessment and Strengthening of Historical Masonry Structures: Ferdowsi High School, Tabriz, Iran

In this study, the seismic vulnerability of the Ferdowsi School building in Tabriz is investigated. The research began with comprehensive fieldwork, during which exploratory surveys and in-depth technical inspections of all structural components were performed. Experimental testing of prismatic masonry specimens was carried out to evaluate their mechanical characteristics, and the resulting properties were then incorporated as input parameters into the numerical model. The seismic vulnerability assessment was then carried out using nonlinear static (pushover) analysis, applying a lateral load pattern proportional to the first vibration mode of the structure. For numerical simulation, the building was modeled in the ABAQUS finite element software using the macro-modeling technique. The results of the nonlinear static analysis indicated that the building does not possess sufficient load-bearing capacity at the target displacement. Damage was primarily concentrated in the form of cracking in the masonry walls as well as in the dome-shaped sections of the roof, requiring the implementation of a seismic retrofitting scheme to enhance the structure’s seismic performance. To rehabilitate the structure, horizontal and vertical reinforced concrete beams were introduced as confining elements for the masonry walls and subsequently applied in the strengthening project. Furthermore, due to the presence of a domed roof at the first-floor level, it was strengthened using FRP composite materials to enhance tensile capacity and ductility. At the second-floor level, where the roof structure is made of timber elements, a steel cable system was employed to improve its strength and diaphragm action. As for the third-floor timber truss roof, the connections were upgraded and reinforced to provide reliable force transmission and to maintain the overall integrity of the structural system. Following the implementation of the retrofitting measures, the structural model was re-analyzed using nonlinear static analysis. The results demonstrated that the proposed strengthening scheme successfully increased the structural capacity up to the target displacement level and satisfied the intended performance requirements. In the final section of the paper, the implementation details of the retrofitting interventions, as well as the practical experiences gained during the implementation process, are presented and discussed.

Development of Load and Resistance Factors for the Reliability based Design of Harbor Facilities

In this study, a Load and Resistance Factor Design (LRFD) method applicable to gravity-type port structures (caisson composite breakwaters and caisson-type quay walls) was developed based on probabilistic reliability analysis methods. To this end, representative domestic design cases distributed across all coastal areas of the East, West, and South coasts were systematically collected and analyzed to evaluate the quantitative failure probability levels for each limit state of the structures. A reasonable target reliability index was established by comprehensively considering the consistency between the results of intrinsic safety margin analyses of existing structures and the reliability indicators of domestic and international design codes. Based on this, code calibrations using the First Order Reliability Method (FORM) and Monte Carlo Simulation (MCS) were performed to determine the optimal load and resistance factors. Applying the proposed load and resistance factors enables the implementation of a rational limit-state design that consistently satisfies the target reliability levels in both structure stability and subgrade design; this is expected to contribute as an advanced technical and academic standard for future revisions to Korea’s reliability-based port design codes.