Marco Di Ludovico

Structural Upgrade Using Basalt Fibers for Concrete Confinement

This paper aims to appraise the opportunities provided by a new class of composites based on using basalt fibers bonded with a cement-based matrix as an innovative strengthening material for confinement of reinforced concrete members. The effectiveness of the proposed technique is assessed by comparing different confinement schemes on concrete cylinders: (1) uniaxial glass-fiber-reinforced polymer (FRP) laminates; (2) alkali-resistant fiberglass grids bonded with a cement-based mortar; (3) bidirectional basalt laminates preimpregnated with epoxy resin or latex and then bonded with a cement-based mortar; and (4) a cement-based mortar jacket. The study showed that confinement based on basalt fibers bonded with a cement-based mortar could be a promising solution to overcome some limitations of epoxy-based FRP laminates.

Shear Strengthening of a PC Bridge Girder with NSM CFRP Rectangular Bars

Bridges worldwide are falling into a state of disrepair caused by deterioration, traffic overloading, and poor maintenance. It is estimated that over 100,000 of the half million existing bridges in the US are in need of repair or replacement. Although the full replacement option could be viable, it is an expensive solution with significant disruption of service. This paper focuses on the use of carbon fiber reinforced polymer (CFRP) rectangular bars installed as near surface mounted (NSM) reinforcement for shear strengthening in conjunction with an externally bonded pre-cured CFRP laminate to increase the flexural capacity of a prestressed concrete (PC) bridge girder. The specimen, which was removed from an overloaded bridge in Kansas was strengthened and tested in the laboratory. Test results showed that the proposed NSM reinforcement technique represents an effective solution to increase shear capacity.

FRP Confinement of Tuff and Clay Brick Columns: Experimental Study and Assessment of Analytical Models

In recent years, fiber-reinforced polymer (FRP) wrapping effectiveness has been clearly confirmed especially with reference to concrete structures. Despite evident advantages of FRP based confinement on members subjected to compressive overloads due to static or seismic actions, the use of such technique in the field of masonry has not been fully explored. Thus, to assess the potential of confinement of masonry columns, the present paper shows the results of an experimental program dealing with 18 square cross sections (listed faced tuff or clay brick) masonry scaled columns subjected to uniaxial compression load. In particular, three different confinement solutions have been experimentally analyzed in order to evaluate and compare the effectiveness of uniaxial glass FRP, carbon FRP, and basalt FRP laminates wrapping. The main experimental outcomes are presented and discussed in the paper considering mechanical behavior of specimens, axial stress-axial strain relationships, and effective strains at failur...

Experimental Investigation of Exterior RC Beam-Column Joints Retrofitted with FRP Systems

Premature brittle failures because of seismic actions strongly affect the behavior of existing reinforced concrete (RC) structural systems. They commonly involve exterior beam-column joints of structures designed without transverse reinforcement. This paper investigates the behavior of unconfined joints that do not conform to current seismic codes and the effectiveness of externally bonded fiber-reinforced polymers (FRPs) as a strengthening technique. It presents an experimental program carried out on six full-scale RC corner joints under constant axial load and transverse cyclic loading in the as-built and FRP-strengthened configuration. After describing the specimen design strategy and test setup, seismic performance is compared. Particular attention is paid to comparing the experimental capacity of as-built joints and the capacity, which can be predicted on the basis of models available in the literature. Finally, a discussion on the effectiveness of different FRP-strengthening layouts is reported.

Nonlinear Analysis of Cross Sections under Axial Load and Biaxial Bending

Biaxial bending moments can reduce the cross section capacity in terms of both strength and ductility. In this paper, a method and an integration procedure is presented that specifically targets the analysis of cross sections under biaxial bending and axial load. The method is applicable to regular or irregular shaped cross sections of various materials internally or externally reinforced by mild steel, prestressing tendons, and fiber-reinforced polymers. Surface integration of meshed cross sections allows moment-curvature relationships to be computed using nonlinear constitutive relationships and three-dimensional interaction domains to be drawn. Iteration procedures and convergence criteria are proposed to rapidly solve the highly nonlinear problem. Numerical tests showed fast convergence of the algorithm and good agreement with experimental results elsewhere. Comparisons between the numerical outcomes and the simplified expressions available in the literature have been performed to indicate the current limits of the formulas in currently available design codes.

Reconstruction process of damaged residential buildings outside historical centres after the L’Aquila earthquake: part I—"light damage" reconstruction

Assessment of the seismic damage and usability of the building stock started a few days after the L’Aquila earthquake in order to evaluate the safety conditions of the buildings concerned. Several ordinances of the Prime Minister were issued to regulate the reconstruction process. In particular, based also on damage level, the procedures for repair, strengthening or demolition/reconstruction of residential buildings were established with the definition of relevant state funding. For each damaged building, practitioners engaged by property owners designed repair and strengthening interventions and then computed the corresponding costs. These projects were the technical basis for funding applications that owners submitted to the government. Technical and financial information collected during the approval procedure of such applications allowed compilation of a database regarding 5775 residential buildings damaged by the L’Aquila earthquake. The present study examines the restoration policy and the procedures regulating the reconstruction process of residential property outside city centres. In particular, the data related to the first phase of the reconstruction process (the so-called “light damage” reconstruction) to recover the usability of slightly damaged buildings are illustrated. The discussion focuses on the time-to-approval of funding applications and on the public contributions granted for repair and local strengthening works.

Empirical fragility curves from damage data on RC buildings after the 2009 L’Aquila earthquake

The study analyses the data related to a database of 7597 private Reinforced Concrete buildings located in the city and the province of L’Aquila surveyed after the 2009 earthquake. Survey data were collected by the Italian Department of Civil Protection during post-earthquake usability inspections including information on building characteristics, level and extent of damage to structural and non-structural components. For each building, the Peak Ground Acceleration demand has been determined according to data available from the ShakeMap of the event and the georeferenced building location. The analysis of data highlights the key role played by the damage to non-structural components—namely, infills and partitions. Damage Grades according to the European Macroseismic Scale EMS-98 have been derived from damage data to single building components. Two building classes have been defined in the study in order to investigate the influence of number of storeys of buildings on the observed damage. Damage Probability Matrices have been derived for the assumed building classes and bins of Peak Ground Acceleration, and observed trends are analyzed. Different methodologies for estimating fragility functions from data on Damage Grades and Peak Ground Acceleration demand are illustrated, discussed and applied to the database, leading to the derivation of EMS-98-based fragility curves for the defined building classes. Finally, the proposed fragility curves are compared with main empirical fragility curves for RC buildings from literature studies.

Repair of Bridge Girders with Composites: Experimental and Analytical Validation

This article reports on a laboratory study undertaken to investigate the flexural behavior of full-scale, damaged prestressed concrete (PC) bridge girders upgraded with externally bonded carbon fiber-reinforced polymer (CFRP) laminates. The study include test on three beams: one was used as the control beam and the other two, damaged by removing the concrete cover and by cutting two and four strands, respectively, were repaired with CFRP laminates. The authors conclude that the upgrade technique used is structurally efficient in providing the damaged beams with stiffness and strength very close to that of the original undamaged beam. They discuss analytical predictions compared to the test results in terms of flexural capacity, deflections, strains, and failure modes. The authors reiterate that the use of CFRP laminates can allow damaged PC girders to recover their original flexural capacity and stiffness.

Hysteretic cyclic response of concrete columns reinforced with smooth bars

The application of smooth (plain) bars in reinforced concrete (RC) construction has been abandoned since the 1970s; however, there are many old reinforced concrete buildings in the world whose construction is based on this old style that are now in need of structural seismic rehabilitation according to the requirements of present day seismic rehabilitation codes. The focus of this study concerns the investigation of the hysteretic cyclic response of RC columns with smooth bars. The results of six column specimens having a variety of details for overlapping splices of longitudinal bars while experiencing two different levels of axial loads under cyclic loading reversals are presented. Through analysis of test observations and the obtained experimental results, it is attempted to clarify major aspects of hysteretic response for RC columns with smooth bars, from a seismic assessment point of view. The hysteretic force–drift responses of columns are deeply investigated and a new concept explaining the flag shape form of the hysteretic response is presented. Furthermore, the rocking response of columns is predicted with a new formulation that assumes an internal compression strut inside the column body as a consequence of rocking that originated from high base rotations. Finally, a simple hysteresis rule is proposed which is the result of considering the combination of two springs in parallel to provide the total hysteretic response as the summation of rocking hysteretic and bottom anchor (smooth bar) hysteretic responses.

FRP Local Retrofit of Non-Conforming RC Beam-Column Joints

Recent seismic events have clearly confirmed the vulnerability of existing reinforced concrete (RC) structures. In particular, field observation of structures damaged by L’Aquila earthquake strongly confirmed that premature failure of partially confined (i.e. exterior) beam-column joints was one of the main causes limiting the global structural seismic capacity. Poor attention to details and a lack of adequate transverse reinforcement typically lead to premature brittle shear failure of joints. To provide support to practitioners involved in the L’Aquila reconstruction process, a proper guideline which illustrates the design of local retrofit interventions on structural and non structural elements has been edited by the Italian Civil Protection Department (DPC) and the Laboratories University Network of Seismic Engineering (ReLUIS). In particular, a viable FRP strengthening strategy to increase the seismic performances of partially confined joints (design procedure and installation steps) is widely discussed and presented in the document. To validate the strengthening system recommended in this guideline, an experimental program has been carried out on as-built and FRP strengthened full scale corner RC joints (T shaped joints). After presenting the main guideline recommendations for local strengthening of existing structures, the paper focuses on the experimental program activity; in particular, the specimen design strategy and test setup definition as well as the comparative analysis of the behavior of tested joints.