M. Di Ludovico

Bond Efficiency of EBR and NSM FRP Systems for Strengthening Concrete Members

This paper reports the results of an experimental program to investigate the bonding behavior of two different types of fiber-reinforced polymer (FRP) systems for strengthening RC members: externally bonded carbon (EBR) plates and bars or strips externally applied with the near-surface-mounted (NSM) technique. The overall experimental program consisted of 18 bond tests on concrete specimens strengthened with EBR carbon plates and 24 bond tests on concrete specimens strengthened with NSM systems (carbon, basalt, and glass bars, and carbon strips). Single shear tests (SST) were carried out on concrete prisms with low compressive strengths to investigate the bonding behavior of existing RC structures strengthened with different types of FRP systems. The performance of each reinforcement system is presented, discussed, and compared in terms of failure mode, debonding load, load-slip relationship, and strain distribution. The findings indicate that the NSM technique could represent a sound alternative to EBR systems because it allows debonding to be delayed, and hence FRP tensile strength to be better exploited.

Experimental Behavior of Nonconforming RC Columns with Plain Bars under Constant Axial Load and Biaxial Bending

AbstractAvailable capacity models for the assessment of seismic capacity of RC columns are mainly based on experimental tests under axial load and uniaxial bending. Furthermore, experimental tests have been mainly performed on columns representative of new constructions. To analyze the effects of biaxial bending on the seismic performances of existing RC columns with design characteristics nonconforming to present day seismic codes and practices, this paper presents the results of a first stage of tests on RC columns under both axial load and biaxial bending, which effectively simulate the seismic actions. In particular, this paper presents results of four tests on full-scale square columns reinforced with plain bars subjected to constant axial load and biaxial cyclic actions. Two different cyclic displacement paths were investigated: horizontal displacements with an inclination angle of 45 or 30°, with respect to the cross-section principal axes. The influence of biaxial bending actions on the global beh...

Cyclic Behavior of Nonconforming Full-Scale RC Columns

Capacity models to assess structural safety are primarily based on experimental outcomes typical of new constructions. In order to analyze deformation and strength mechanisms of members that do not comply to current seismic codes and practices, an experimental investigation was undertaken on full-scale columns reinforced with deformed or plain rebars. The experiments involved eight tests under monotonic or cyclic actions on square or rectangular reinforced concrete columns designed according to provisions, construction practice, and material properties enforced between the 1940s and 1970s. Experimental outcomes allowed pointing out global and local behavior of RC columns typically found in existing constructions, in which both plain and deformed bars can be found. Theoretical plastic rotation capacities provided by the proposed supplement to the current ASCE standard are discussed in this paper and compared to those experimentally obtained. The results indicate that predicted plastic rotations corresponding to significant loss of lateral-force capacity are very conservative if compared with experimental outcomes. This seems especially clear in the case of columns reinforced with plain rebars. For these columns, the contribution of the base rotation on the global deformation mechanism is considerable.

FRP Strengthening of Full-Scale PC Girders

Every year, several prestressed concrete (PC) bridge girders are accidentally damaged by overheight vehicles or construction equipment impact. Although complete replacement is sometimes deemed necessary, repair and rehabilitation can be far more economical, especially when the time and the installation cost of the repair system are drastically reduced. The use of fiber-reinforced polymer (FRP) composites to restore the original capacity of impacted PC girders are being increasingly considered for bridge applications due to their high strength-to-weight ratios, corrosion and fatigue resistance, their ease of transport and handling and their potential for tailorability. Experimental data on full-scale PC girders strengthened by using FRP laminates are very limited; the present paper is intended as an extension of a previous experimental work conducted by writers [as reported by M. Di Ludovico et al. ACI Struct. J. 102(5), 97–109 (2005)] on three full-scale PC specimens. In particular, tests on five full-sca...

Masonry Reinforcement with IMG Composites: Experimental Investigation

The interest in strengthening of historical masonry structures is significantly grown especially to techniques which combine properties like as reversibility, compatibility, and sustainability of the intervention. Among these, a promising technique is the use of inorganic matrix grid (IMG) composites. Several experimental tests have been carried out to prove the effectiveness of this system as a strengthening solution for different masonry types. The present paper presents the original results of five tests on uncoursed stone masonry panels under diagonal compression and collect the data of previous tests carried out by the authors on other masonry typologies. The tests results on several masonry types and strengthening layouts as well as Fiber reinforced Polymer (FRP) grid and mortar types are reported and discussed. The experimental programs clearly confirmed the effectiveness of the investigated strengthening technique to increase the panels shear capacity and ductility; however, a suitable theoretical expression to quantify the benefits provided by this strengthening solution, based on the reinforcement layout and on the masonry type, is still missing. The comparative analysis of the experimental data is presented in the paper in order to clarify the benefits provided by each strengthening system.

Life-cycle cost optimization of the seismic retrofit of existing RC structures

The life-cycle cost analysis of buildings prone to seismic risk is a critical issue in structural engineering. Expected loss, including damage and repair costs, is an important parameter for structural design. The combination of economic theory and computer technology allows for a more developed approach to the design and construction of structures than ever before. In this study, a simplified method based on a semi-probabilistic methodology is developed to evaluate the economic performance of a building prone to seismic risk. The proposed approach aims to identify the most cost-effective strengthening strategies and strengthening levels for existing structures during their structural lifetime. To achieve this, the method identifies the optimal strengthening level, computing on the one hand the costs of strengthening the structure at different performance levels for each strategy, and, on the other, the expected seismic loss during the structure’s lifetime. To assess the expected loss, the building is divided into several components, both structural and non-structural. A set of fragility curves is assigned for each component. Then, once the structural model and the various components of the building, with the corresponding fragility curves, are defined, a loss assessment is performed using a static non-linear analysis. The summation of the strengthening costs and the discounted expected losses produces a relationship between the total costs and the strengthening level. The minimum of this relationship identifies the most cost-effective strengthening intervention. As a case study, this method is applied to an existing reinforced concrete (RC) structure severely damaged by the 2009 earthquake in L’Aquila. Different strategies are analyzed, namely the FRP (fiber reinforced polymer) strengthening of elements, the RC jacketing of columns, RC exterior shear wall insertions, and the base isolation of the building.

Remarks on damage and response of school buildings after the Central Italy earthquake sequence

The seismic assessment of the vulnerability of existing public structures, especially school buildings, is a crucial issue in seismic prone countries. Recently, several national and regional programs and activities have focussed on the mitigation of Italian public buildings. They promote the scheduling of public buildings’ structural safety assessment and, when needed, the design and execution of strengthening interventions. Nevertheless, the three strong earthquakes that occurred in the last decade in Italy, Abruzzo (2009), Emilia (2012), and Central Italy (2016), confirmed the vulnerability of school buildings and the social importance of their quick re-opening after a damaging earthquake. In the present paper, the activities carried out on 1514 school building structures in the aftermath of the 2016 Central Italy earthquake sequence are reported and analysed. According to survey data collected by post-earthquake usability inspections, the paper analyses the school buildings characteristics, damage level and extent to structural and non-structural components as well as the correlation between seismic intensity and observed damage.

Estimation of repair costs for RC and masonry residential buildings based on damage data collected by post-earthquake visual inspection

In the immediate post-earthquake, the safety conditions of buildings are commonly evaluated by field visual inspections. Then, a second phase involves the design of repair interventions and the relevant funding requests to the government or to insurance companies. The paper discusses the data related to the 2009 L’Aquila earthquake, focusing on the empirical damage and relevant Actual Repair Costs (ARC) of damaged residential buildings derived from requests for funding presented by practitioners engaged by owners in the reconstruction process. In particular, the data collected from a set of 2500 residential Reinforced Concrete (RC) and masonry buildings are presented focussing on the construction age, number of storeys, damage extent on structural components and ARC. A damage index for each building component has been computed according to data collected by field inspections and the relationship between damage index and different classes of buildings is herein outlined. Then, a correlation between the empirical damage and ARC is determined by means of a regression analysis. The proposed relationship between empirical damage and ARC may drive decision makers, in the immediate post-earthquake, to make preliminary estimates of the repair costs, only based on quick surveys on residential buildings. The relationship may also be used as a tool to figure out repair costs based on damage scenarios.

Damage assessment and the effectiveness of prevention: the response of ordinary unreinforced masonry buildings in Norcia during the Central Italy 2016–2017 seismic sequence

Four regions of central Italy were struck by the seismic sequence of the 2016 earthquake in the country: Lazio, Abruzzo, Umbria and Marche. This highlighted the different behaviour of masonry constructions depending on the prevention actions carried out after previous earthquakes. In particular, although damaged, the masonry buildings in the historical centre of Norcia (Umbria region) behaved significantly better than those in other regions. Indeed, the strengthening interventions carried out after the earthquakes of 1971, 1979 and 1997 greatly affected the seismic behaviour of masonry aggregates (contiguous masonry structural units, MSUs) in the historical centre, which sustained limited damage and a low number of collapses. This paper discusses the empirical data on damage collected with respect to 670 MSUs by means of the first level survey form concerning post-earthquake damage, and usability assessments (AeDES). The forms completed for the survey relate to MSUs in the historical centre of Norcia and were produced by the technicians of the Umbria Seismic Risk Office. The analysis shows the correlation between the MSU characteristics of: age of construction and renovation work; type of vertical and horizontal structures; roof types and usability rating; and the damage level and extent thereof detected in vertical structures. The effectiveness of previous strengthening interventions and the analyses of the types of strengthening solution are also discussed. A case study aggregate is analyzed in detail in order to illustrate the importance of strengthening interventions on vertical bearing elements. The strengthening interventions resulted in a sound strategy to strongly reduce losses, even in a very vulnerable centre comprised of old residential masonry aggregates.

Digital human models for gait analysis: experimental validation of static force analysis tools under dynamic conditions

This work explores the use of an industry-oriented digital human modelling tool for the estimation of the musculoskeletal loads corresponding to a simulated human activity. The error in using a static analysis tool for measuring articulations loads under not-static conditions is assessed with reference to an accurate dynamic model and data from real experiments. Results show that, for slow movements, static analysis tools provide good approximation of the actual loads affecting human musculoskeletal system during walking.