Mario D'Aniello

Experimental analysis of steel dissipative bracing systems for seismic upgrading

Abstract Energy dissipating devices, such as metallic ductile dampers, could represent one reliable system for seismic performance upgrading of reinforced concrete (RC) structures. This paper illustrates the significant improvement to the seismic response of RC structures equipped with dissipative bracing systems, such as eccentric braces (EBs) and buckling restrained braces (BRBs). In fact, the results of experimental tests carried out on two similar two‐storey one‐bay RC structures, respectively equipped with EBs and BRBs, are described. Referring to EBs, 3 lateral loading tests have been performed. Each test is characterized by shear links with bolted end‐plate connections. Different design criteria have been applied in the design of the connections. In the first test, capacity design criteria have not been considered. In the second test, a capacity design criterion has been applied, with a link shear over‐strength factor equal to 1.5. In the third test, a design criterion similar to the one adopted fo...

Experimental Tests of a Real Building Seismically Retrofitted by Special Buckling‐Restrained Braces

Buckling Restrained Braces (BRBs), differently from conventional braces, do not exhibit appreciable difference between the tensile and compression capacity and no strength degradation of brace capacity under compressive and cyclic loading. Since lateral and local buckling behaviour modes are restrained, large inelastic capacities are attainable. Hence, BRBs may represent an efficient and reliable solution for reducing the seismic vulnerability of buildings. Results of experimental tests on the response of a real two‐story reinforced concrete (RC) building equipped with BRBs are presented and discussed. The considered BRBs are a special ‘only‐steel’ version of the more common ‘unbonded braces’. In particular, two different BRBs have been tested. Both of them are detachable “only‐steel” devices, consisting in a rectangular steel plate and a restraining steel sleeve. The latter is composed by two omega shapes which are bolted together. The main characteristic of the braces consists in the possibility to hide...

Seismic Upgrading of Steel Moment-Resisting Frames by Means of Friction Devices

In recent decades, several passive energy dissipation systems have been conceived in order to minimize the damage in structural and non-structural components of either new or existing buildings. In this study, the use of friction damped tension-compression diagonal braces for seismic upgrading of a steel moment resisting frames is investigated. To this aim, nonlinear time history analyses have been carried out on a set of representative frames with and without friction damped braces. In the nonlinear time history analyses, two sets of natural accelerograms compatible with seismic hazard levels of 10% and 2% probability of exceedance in 50 years have been considered. Under these records, the structural re- sponse has been comparatively investigated in terms of the maximum inter-storey drift ratio, maximum storey accelera- tion, residual drift ratio and displacement demand for the friction device. The results clearly highlighted that the applica- tion of friction damped braces allows reducing the damages to the main structural elements, thus significantly improving the seismic behaviour of the frame.

Remarks on Seismic Design Rules of EC8 for Inverted-V CBFs

Chevron concentrically braced frames (C-CBFs) are expected to provide limited ductility in the framework of Eurocode 8: differently from North American codes, lower values of behavior factors are recommended by EN 1998 for C-CBFs than for other concentric bracing configurations (namely diagonal and cross bracings). The research presented in this paper is aimed at revising the design rules and requirements provided for by EN 1998-1 for C-CBFs in order to improve the ductility and the dissipative capacity of this structural system. The proposed design criteria are validated by means of nonlinear dynamic analyses performed on a study case. The results confirm the effectiveness of developed design procedure.

FINITE ELEMENT ANALYSES ON FREE FROM DAMAGE SEISMIC RESISTING BEAM-TO-COLUMN JOINTS

The seismic design strategy implemented in current codes is based on the capacity design principles that allow the formation of plastic hinges into predefined parts of the structure. Therefore, significant damage is expected at ultimate limit state, to which high repair costs are associated. Recently, new design strategies have been proposed in order to avoid the damage of the structure. The most of them are grouped into two categories, namely i) using special damping devices introduced in the structure as additional resisting element; ii) changing the dissipation mechanism of the structure by means of friction-based dissipative joints. The second possibility is promising and really effective because it guarantees no architectural interference if adopted for moment-resisting frames (MRFs), and low forces transferred to the foundations. The novelty of free from damage (FREEDAM) joints lays in the fact that the energy is dissipated by friction at the interface between plates in contact instead of the classical plastic deformation energy dissipation mechanism. In this paper, the seismic behaviour of FREEDAM joints is investigated by means of parametric finite element analyses carried out in order to examine the influence of geometric and mechanical feature of the friction device (e.g. position of friction plane, type of friction interface, bolt clamping, bolt strength). The accuracy of finite element models is also validated on the basis of some experimental tests. 802 Available online at www.eccomasproceedia.org Eccomas Proceedia COMPDYN (2017) 802-814

Finite Element Analysis of Composite Replaceable Short Links

Eccentrically braced frames (EBF) with detachable short links are an efficient solution for buildings in seismic areas owing to their high energy dissipation capacity and ductility and ease of repair in the earthquake aftermath. Past studies revealed that short links can develop shear overstrength (i.e. Vu/Vp, where Vu is the ultimate shear strength and Vp the corresponding plastic resistance) larger than the value recommended in EC8 [1] (i.e. Vu/Vp =1.5). One of the factors causing the higher shear overstrength is the presence of axial restraints that leads to the development of tensile forces in the link at large levels of rotation. Another reason for higher shear overstrength is the composite slab that can resist the shear distortion together with the short link. Within the DUAREM project [2], full scale pseudo-dynamic experimental tests were carried out on 3D EBF allowing thus the investigation of replaceable links considering two arrangements: (i) steel solution – the link was uncoupled from the slab (ii) composite solution – the slab and link are connected. The aim of this paper is to present the results of finite element analyses (FEAs), based on calibrated models and the comparison between the obtained results and the experimental tests performed by [2]. The numerical investigation carried out aims to evaluate the shear overstrength and the level of axial force in the link for both tested configurations.

Experimental Tests on Extended Stiffened End-Plate Joints within Equal Joints Project

Bolted extended stiffened end-plate beam-to-column joints are commonly used for steel moment resisting frames in seismic areas. In the framework of European codes, EN 1993:1-8 provides the design rules and the analytical models to predict the mechanical behavior of the joints. On the other hand, EN 1998-1 specifies the required performance for seismic resistant joints. Within EQUALJOINTS project design rules have been developed and experimental tests were carried out to seismically prequalify extended stiffened end-plate joints. In this paper the proposed design rules are discussed and results of the experimental tests are described.

FINITE ELEMENT ANALYSES ON SEISMIC RESPONSE OF PARTIAL STRENGTH EXTENDED STIFFENED JOINTS

Extended stiffened end-plate bolted joints are widely used in seismic resistant steel frames. In the United States (US) this type of joint is seismically pre-qualified according to AISC 358. In Europe within the framework of the ongoing EQUALJOINT research project, prequalification criteria for different types of bolted joints are under development. Differently from the US approach, in the EQUALJOINT procedure both full and partial strength joints are seismically qualified. The experimental tests carried out within the EQUALJOINT project confirmed the effectiveness of these intermediate strength levels. Therefore, the aim of this work is investigate the possibility to extend this design approach to US joints. The results of a comprehensive parametric finite element investigation are described and discussed, showing the effectiveness of the proposed design performance criteria. 4952 Available online at www.eccomasproceedia.org Eccomas Proceedia COMPDYN (2017) 4952-4964

FINITE ELEMENT MODELLING OF DETACHABLE SHORT LINKS

Eccentrically braced frames with replaceable links are viable seismic resisting systems that guarantee large dissipative capacity and quick and easy replacement of the damaged dissipative zones after seismic events, thus reducing the repair costs. Experimental tests carried out within DUAREM research project [12] demonstrated the high effectiveness of this system and highlighted the importance of the bolted connections of the shear links on the system response at both global and local level. In order to investigate the behaviour of the tested detachable links, finite element analyses have been carried out. The finite element (FE) models are calibrated on the basis of the experimental response curves in terms of the shear force and link rotation. Once calibrated the finite element models, several parameters have been investigated such as the type of pre-loadable bolts (i.e. HR and HV), the level of bolt clamping force, the boundary conditions, the presence of constructional tolerances (e.g. initial gap between end-plate at both link ends). The results from the parametric study enables the characterization of the shear and axial force interaction on the link end connections. 790 Available online at www.eccomasproceedia.org Eccomas Proceedia COMPDYN (2017) 790-801

Preliminary Finite Element Analyses on Seismic Resistant FREE from DAMage Beam to Column Joints under Impact Loading

Nowadays, the interest on structural robustness is increasing because of the recent terroristic attacks. Although a large number of research projects have been carried out in this field, limited design guidelines as well as code recommendations are nowadays available. Leading to the fact that the design for robustness is far from being current practice. Conversely, the design for natural hazards as the earthquake is a well-consolidated practice and modern codes implement effective and well-recognized design rules. Even though seismic design philosophy based on the concept of hierarchy of resistance enables structural robustness for conventional structural systems, this is not demonstrated for structures equipped with anti-seismic devices as well as innovative dissipative systems. Recently, the use of friction based dissipative joints has been proved to be a promising solution for seismically design steel moment resisting frames. However, the robustness and the resistance against impact loading of this type of joints is not yet investigated. With the aim to develop an experimental campaign based on impact tests, preliminary finite element analyses have been carried out to identify the main criticisms and to drive the rational design of the joint specimens. With this regard, in the present paper, the results of a numerical parametric study on the preliminary push-down test are presented and discussed.