Bulletin of Earthquake Engineering

Năng lực chống động đất của ba công trình gạch không có armature hiện đại bị ảnh hưởng bởi chuỗi trận động đất tháng 5 năm 2012 tại Emilia (Ý) đã được nghiên cứu, nhằm xác định các biên độ an toàn và các vấn đề có thể gặp trong thiết kế chống động đất theo các quy định của châu Âu. Các công trình được chọn đã được thiết kế lại, áp dụng phân tích tĩnh tuyến tính và phi tuyến tính, và được kiểm tra khả năng sụp đổ theo cả Eurocodes 6 và 8 cũng như các quy định xây dựng của Ý. Thiết kế đưa ra kết quả không nhất quán, đặc biệt là với việc áp dụng Eurocodes, khi mà không có công trình nào trong số ba công trình đạt được yêu cầu an toàn ngay cả với hành động bên thấp. Mặc dù vậy, hai trong số các công trình này không gặp bất kỳ hư hỏng thấy được nào sau các sự kiện tháng 5 năm 2012. Các yêu cầu của tiêu chuẩn chống động đất Ý, ít nhất là đối với các phân tích tĩnh phi tuyến, đã cung cấp kết quả phù hợp hơn với phản ứng thực tế của các công trình trước động đất. Cuối cùng, các vấn đề chính và một số đề xuất cải tiến quy trình quy định cho thiết kế động đất của các công trình gạch không có armature được thảo luận.

This paper focuses on seismic fragility and damage scenario assessment of minor Italian historical centres through the development of urban fragility curves. With reference to the case study of Balvano, a small centre located in Basilicata Region of Italy, two hybrid models have been adopted. The first is a mechanic-based hybrid model developed by the authors to derive urban fragility curves specifically; the second is the macroseismic method, originally conceived to derive typological fragility curves for single building classes, expanded to derive urban fragility curve herein. Balvano was strongly struck by 1980 Irpinia-Basilicata earthquake (Ms = 6.90) and hence subjected to an intense reconstruction process during 1980s, where almost the 80% of the buildings were reconstructed with reinforced concrete structures in the place of unreinforced masonry ones. Seismic vulnerability and damage scenarios before and after 1980 have been assessed and compared with the purpose of validating the effectiveness of the urban scale fragility curves obtained through hybrid methodologies and quantifying the effect of the ‘new’ seismic hazard maps and first seismic codes and recommendations released by the Italian Government in the aftermath of 1980 for the construction of new buildings or for retrofitting the existing ones. A good matching between predicted and occurred damage scenario from the research outcomes emerged, confirming the effectiveness of the urban scale hybrid fragility curves to assess seismic vulnerability at urban scale. Moreover, the comparison of the damage scenarios pre and post-reconstruction highlighted the crucial role played by the code prescriptions adopted in that years for reducing the seismic vulnerability of the municipality and the importance of the ‘new’ seismic hazard maps introduced in 1980s. Finally, the differences between mechanical-based hybrid and macroseismic model have been discussed in the paper.

The advantages of passive supplemental dampers for performance enhancement of new and existing structures have been demonstrated extensively in the past. The big amount of experimental tests carried out all over the world on framed structures upgraded by energy dissipating bracing (EDB) systems based on hysteretic dampers (HDs), have shown their effectiveness in reducing seismic effects on buildings. The mechanical characteristics of the HDs in some cases may be different from those arising by the design procedure due to industrial tolerance or because of some damage suffered during previous earthquakes. In order to assess the robustness of this technique, in terms of capacity of seismic vibrations control even for significant changes in the mechanical characteristics of the EDB system respect to the design ones, in this paper experimental tests and parametric nonlinear time history analysis have been carried out changing the characteristics of the HD stiffness and strength. The experimental results refer to the shaking table tests performed at the Structural Laboratory of the University of Basilicata within a wide research program, named Joint Experimental Testing on Passive and semiActive Control Systems. The program has been completely funded by the Italian Department of Civil Protection within the activity of the Research Line 7 of the ReLUIS (Italian Network of University Laboratories of Earthquake Engineering) 2005–2008 project. A displacement-focused design procedure has been considered to evaluate the mechanical characteristics of the dissipating system, with the aim of limiting inter-storey drifts after frame yielding. From the experimental point of view, two design solutions have been tested for chevron braces equipped with HD, assuming the same stiffness but different values of both ductility demand and yield strength of the HDs. Moreover, parametric studies have been performed through numerical simulations. This paper provides an overview of the experimental set up and briefly summarizes the experimental outcomes and the comparison with the results of numerical nonlinear time history analysis. Moreover, the results of the parametric analysis for the assessment of the performances of the dissipating system in controlling structural response are presented.

Energy-based seismic design is being rapidly developed and suggests that the seismic demands are met by the energy dissipation capacity of the structural members. Equivalent damping ratio is a measure of energy dissipation in structural members that accounts for the post-elastic behavior of the member and provides insight regarding the dynamic response reduction during a seismic event. The present study implements a machine learning algorithm to estimate the equivalent damping ratio in reinforced concrete shear walls at displacements corresponding to a 1.0% lateral drift ratio. Five different machine learning models, namely, Robust Linear Regression, K-Nearest Neighbor Regression, Kernel Ridge Regression, Support Vector Regression, and Gaussian process regression were evaluated in order to choose the model with the highest accuracy. Among all models, Gaussian process regression, a machine learning method with successful implementation experiences in civil/structural engineering related problems, is selected to identify the equivalent damping ratio. The developed GPR-based algorithm uses a database of 161 rectangular shear walls subjected to quasi-static reversed cyclic loading with geometry and mechanical properties commonly found in building stocks of many earthquake-prone countries. The proposed algorithm estimates the equivalent damping ratio for each specimen by predicting the cyclic dissipated energy and lateral force values as two dependent variables. The model validation results show a mean coefficient of determination (R2) of about 0.89; a relative root mean square error of about 0.14 and a mean absolute percentage error of 10.44%, which is considered a substantially accurate prediction for such a complex problem. An open-source model and the entire database are provided which can be used by researchers and also design engineers. The proposed predictive model enables comparing the damping capacity of shear walls and the outcomes of this study are believed to contribute to the energy-based design or performance evaluation procedures in terms of predicting the energy capacity of shear walls.

Damage observed in existing structures after recent earthquake events pointed out the key importance of beam-to-column joints in influencing the global response of reinforced concrete structures. In the last two decades several theoretical and empirical models have been proposed for evaluating shear strength of beam-to-column joints. The present paper reports an overview of the models currently available in the scientific literature for evaluating shear capacity of exterior beam-to-column joints. The present study is the first step of a wide analysis aimed at assessing such models and improving them. Moreover, the uncertainties deriving by applying the mentioned models will be also quantified therein, by means of well-established procedures for probabilistic seismic analysis of structures. The final results of that study are reported within a companion paper.