Month: June 2021

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Nowadays, Buckling-Restrained Braced Frames (BRBF) are mainly used as lateral load-resisting systems in seismic areas. Two characteristics of higher energy dissipation capacity and lack of existence of buckling behavior have been caused that buckling-restrained brace to be a better alternative to conventional bracing. In this study, the response modification factor (R-factor) and other parameters of buckling of Reinforced Concrete Frame (RCF) with BRB bracing (RCF-BRB) have been investigated. The (R-factor) is a function of different parameters, which to determine these coefficients, the nonlinear static pushover analysis in accordance with ATC-19 and two methods of equal energy and Priestley & Paulay were used to evaluate the plastic behavior of RCF with and without BRB bracing. The result showed that the lateral stiffness of RCF-BRB decreases with increasing the number of stories so that in the number of high stories, the lateral stiffness of RCF-BRB becomes very close to the lateral stiffness of the RCF.

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A numerical campaign comparing the seismic behavior of cold-formed steel rack structures using both Nonlinear Static Analysis (NSA) and Incremental Dynamic Analyses (IDA) is presented. A total of 140 progressively scaled natural ground-motion records, along with 2 different forces distribution for NSA, were applied to a case study model build considering geometrical nonlinearity ( –  effects) and using proper elements to reproduce the pinching of beam-to-column joints in case of hogging and sagging bending moment. Data obtained from IDA were statistically processed and compared with the ones from NSA in terms of seismic vulnerability, specifically in terms of displacement demand and capacity, collapse spectral acceleration and proposing an appropriate damage index capable of tracking the state of the system as the spectral acceleration increase. Results show that NSA underestimates the displacement demand of the system and overestimates the collapse intensity measure (capacity spectral acceleration), thus not always being on the safe side.

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The study presents an experimental and numerical assessment of the Prestressed Lead Extrusion Damper (P-LED), an emerging energy dissipation device which provides energy dissipation through the plastic extrusion of lead, and achieves high specific output force by preloading of the working material. Tests are performed according to the European standard EN 15129. The damper shows a rigid-plastic behaviour with an essentially rectangular hysteresis loop, resulting in an effective damping of 0.55 regardless of the imposed deflection, and is able to sustain multiple cycles of deformation at the basic design earthquake displacement without degradation of the output, providing maintenance-free operation even in presence of repeated ground shakes. A 3D finite element model of the P-LED is formulated and used in a parametric study to investigate the influence of the device dimensions on the output force. The numerical data points are fitted by a simple model which can be used for designing the damper to a specified quasi-static force.

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Retrofit solutions conceived to have low-invasiveness, rapidity of execution and seismic capacity enhancement are of paramount importance in the perspective of Performance-Based Retrofit. Among the various retrofit techniques developed for existing reinforced concrete buildings, those based on the use of external additive walls seem to better satisfy such prerequisites.

This paper deals with a preliminary numerical study aimed at investigating the benefits provided by external post-tensioned rocking Cross-Laminated Timber (CLT) walls to an existing six-storey reinforced concrete building. To this aim, a design methodology based on the Displacement-Based Design which allows to determines the wall dimensions and the pre-stressing forces in the tendons has been herein proposed.

The effectiveness of the additional rocking CLT walls have been validated trough nonlinear static analyses, conducted on both as-built and retrofitted structure. Preliminary results, show that the retrofit intervention is beneficial in terms of seismic capacity increase, expected annual losses and reduction of the seismic risk class of the construction. Nevertheless, future studies based on a more accurate modelling are necessary to validate the results herein obtained and for defining technological solution the connections between framed structure and CLT walls.

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