Carmine Lima

Capacity models for shear strength of exterior joints in RC frames: state-of-the-art and synoptic examination

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.

Capacity models for shear strength of exterior joints in RC frames: experimental assessment and recalibration

Several theoretical models are currently available in the scientific literature for evaluating the shear capacity of both exterior and interior beam-to-column joints in reinforced concrete (RC) frames. A reasonably wide set of those models, based on either analytical or empirical formulations, has been summarised within a companion work. The present paper firstly presents a wide database which collects results obtained in about two-hundred experimental tests carried out on RC joints. Those results are employed for assessing the above mentioned capacity models by considering a set of experimental data much wider than those usually utilised in the original formulation of such models. Accuracy and reliability of the various models are measured by quantifying some statistical parameters actually describing the relationship between the experimental evidence and the prediction of the various capacity models under consideration. Three relevant classes of joints (namely unreinforced, under reinforced and code-compliant) are considered with the aim of emphasising that the various models perform in a rather different way when applied to those different classes. Finally, a possible recalibration of the various models is proposed with the objective of enhancing their predictive capacity with respect to both the database as a whole and the three classes of RC joints mentioned above.

Cost-competitive Steel Devices for Seismic Retrofitting of RC Frames: Model Identification and Nonlinear Analysis

Seismic retrofitting of existing reinforced concrete (RC) buildings, designed in the last decades in seismic areas, is one of the most complex tasks for structural engineers: in fact, it includes several issues, such as quantifying the capacity of existing members, designing the supplemental ones and analysing the whole structure. This paper is intended as a contribution to clarifying some of those issues. First of all, a model based on using 1D finite elements with fiber section discretization is proposed for simulating the behaviour of a cost-competitive steel device that can be employed as a link in Y-shaped eccentric bracings (EB): particularly, the cyclic response and the low-cycle fatigue degradation is modelled, based on the results of obtained in a previous experimental research carried out at the University of Salerno. Secondly, the global response of an existing RC frame equipped with the aforementioned devices is investigated via Non Linear Time History (NLTH) analyses. Taking into account the lowcycle fatigue often leads to significantly more severe seismic displacement demand value on the retrofitted structure: a close correlation is unveiled between some specific features of the seismic signals adopted in the NLTH and the actual influence of low-cycle fatigue.

Concrete with Recycled Aggregates: Experimental Investigations

The mechanical behaviour of Recycled Aggregate Concrete (RAC) is investigated by reporting the main results of experimental tests intended at understanding the influence of Recycled Concrete Aggregates (RCAs) on the resulting mechanical properties of concrete. The focus is placed on the higher porosity of RCAs and their higher water absorption capacity. Consequently, the role of the initial moisture conditions of RCAs at mixing is also unveiled and its consequences on both the hydration reaction and the time evolution of compressive strength are highlighted. The influence of processing procedures intended at reducing the aforementioned porosity is also discussed.

Cement Replacement: Experimental Results for Concrete with Recycled Aggregates and Fly-Ash

The experimental activity reported in this chapter was aimed at enhancing the knowledge about the mechanical behaviour and durability of concretes made with Recycled Concrete Aggregates (RCAs) and coal Fly Ash (FA) and their possible use for structural purposes. To this end, starting from a reference concrete composition, twelve mixtures were designed by replacing part of the ordinary constituents (i.e. cement, sand and coarse aggregates) with the FA and RCAs. The time evolution of the compressive strength, as well as the splitting strength, were measured with the aim to monitor the mechanical performance, whereas the durability performance was scrutinised by measuring water permeability, carbonation depth and chloride-ions ingress. The obtained results unveil the influence of both RCAs and FA on the resulting concrete performance and highlight that their combined use can lead to a synergistic effect in terms of the relevant physical and mechanical properties of structural concrete.

RATIONAL SEISMIC RETROFITTING OF RC STRUCTURES BASED ON GENETIC ALGORITHMS

This paper presents a rational strategy developed for optimizing seismic retrofitting of Reinforced Concrete (RC) frames. It is based on combing memberand structure-level techniques in order to achieve optimal design objectives within a multi-level PerformanceBased approach. On the one hand, in principle, confinement with composite materials, steel and/or concrete jacketing might be considered as a member-level technique capable to enhance the capacity of under-designed members and, consequently, of the structure as a whole. On the other hand, introducing steel bracing systems or shear walls might be taken into account as structure-level techniques. Generally, memberand structure-level techniques are not employed together in seismic retrofitting or, in the cases in which they are combined, no well-established rules are available for choosing their optimal combination. However, a synergistic use of such techniques by means of well-defined procedures could help designers obtain optimal seismic retrofitting performance. The latest progresses about a procedure developed by the authors for selecting the optimal retrofitting solution among the technically feasible ones, obtained by combining alternative configurations of steel bracing systems and FRP-confinement of critical members, are presented herein. Specifically, the main aspects about formulating a genetic algorithm capable to select the “fittest” retrofitting solution is implemented and summarised. The main assumptions about the representations of “individuals” as part of this genetic algorithm and the main information about the generic operations (i.e. selection, crossover and mutation) are outlined. Finally, the procedure is applied to a 3D frame with the aim to demonstrate its potential. 4194 Available online at www.eccomasproceedia.org Eccomas Proceedia COMPDYN (2017) 4194-4212

NONLINEAR STATIC ANALYSIS OF INFILLED RC FRAMES: A NOVEL SIMPLIFIED PROCEDURE

Abstract. Masonry walls are generally utilized in Reinforced Concrete (RC) structures, either as external infills or as internal partitions. Although the interaction between them and structural members significantly affects the seismic response of structures, infills are usually not included in the structural models and, hence, their mechanical contribution is neglected in seismic analysis and assessment of existing structures. However, additional strength provided by infills may either play a beneficial role or affect the resulting structural capacity. Although several proposals are currently available for simulating the nonlinear response of masonry infills in structural analysis, no well-established methods emerged so far for evaluating the global response of infilled RC frames. This paper proposes a simplified procedure based on Nonlinear Static (NLS) analysis and an extension of the well-known N2 Method. A statistical assessment and validation is also presented with the aim to confirm accuracy and reliability of the proposed analysis procedure.

Comparative Application of Capacity Models for Seismic Vulnerability Evaluation of Existing RC Structures

Seismic vulnerability assessment of existing buildings is one of the most common tasks in which Structural Engineers are currently engaged. Since, its is often a preliminary step to approach the issue of how to retrofit non‐seismic designed and detailed structures, it plays a key role in the successful choice of the most suitable strengthening technique. In this framework, the basic information for both seismic assessment and retrofitting is related to the formulation of capacity models for structural members. Plenty of proposals, often contradictory under the quantitative standpoint, are currently available within the technical and scientific literature for defining the structural capacity in terms of force and displacements, possibly with reference to different parameters representing the seismic response. The present paper shortly reviews some of the models for capacity of RC members and compare them with reference to two case studies assumed as representative of a wide class of existing buildings.