Franco Braga

Bio: Franco Braga is an academic researcher from Sapienza University of Rome. The author has contributed to research in topics: Seismic risk & Corrosion. The author has an hindex of 12, co-authored 43 publications receiving 683 citations. Previous affiliations of Franco Braga include University of Basilicata.

Performance of non-structural elements in RC buildings during the L’Aquila, 2009 earthquake

Abstract: In Italy infills and partitions (non-structural elements) are typically made up of hollow brick masonry, disposed in one or two parallel vertical walls. Many studies have analysed their role on the seismic behaviour of moment resisting framed RC buildings and many seismic codes, all over the world, have provided specific additional measures for them. During the Abruzzo seismic sequence, non-structural damage in RC buildings, both private and public, was extensive, varying from small cracks to collapse, along with minor or no damage to structural elements. This damage involved a number of buildings, both old and recently completed, determining heavy socio-economic consequences, including human casualties, loss of building functionality (particularly important in case of strategic constructions), and unusable buildings. In this paper a review of the most frequent damage patterns is performed, aimed at identifying the main causes of damage and linking them to commonly adopted construction rules. For this purpose, local and global structural configurations frequently exhibiting non-structural damage are described, aside from out-of-plane and in-plane failures. Furthermore, a review of code provisions on non structural elements has been performed in the paper making reference to the most prominent current seismic codes and, finally, some design and construction rules are suggested.

Analytical Stress—Strain Relationship for Concrete Confined by Steel Stirrups and/or FRP Jackets

Abstract: This paper presents a plain strain analytical model, based on the elasticity theory, to determine the confining pressures of transverse reinforcements on the concrete core of a reinforced concrete member. The analytical evaluation of the confining pressures was first carried out on reinforced sections with square and circular stirrups, and subsequently on reinforcement configurations of greater complexity with square and rectangular stirrups and supplementary cross ties. Finally, the model has been used to evaluate the confining pressures applied by external wrapping in any material [fiber-reinforced polymer (FRP), S-glass, steel, etc.] and to design better combinations of techniques and confinement materials. In order to obtain the stress–strain curves due to passive confinement, an analogy between square and circular sections has been introduced. In this way, any active confinement model derived by triaxial tests on cylindrical specimens can be used. The model has been validated by comparing its predict...

Modified Steel Bar Model Incorporating Bond-Slip for Seismic Assessment of Concrete Structures

Abstract: This paper presents a simplified model for describing the response of a longitudinal bar embedded in concrete, taking into account the bond-slip phenomenon. The model is developed by assuming a linear bond-slip field along the bar anchorage length and provides a simplified stress-strain relationship to assign to the longitudinal reinforcement. The analytical approach adopted makes the proposed model very convenient from a computational standpoint because, unlike many other refined models, it does not require a multilevel iterative process. Moreover, the assumptions made are particularly appropriate for modeling bond-slip of smooth bars generally used in older reinforced concrete buildings. The implementation strategy of the proposed bond-slip model in general-purpose nonlinear structural analysis software and comparisons with experimental results are discussed in a companion paper.

Speedup of post earthquake community recovery: the case of precast industrial buildings after the Emilia 2012 earthquake

Abstract: The Emilia, May–July 2012, earthquake hit a highly industrialized area, where some tens thousands industrial buldings, mainly single storey precast structures, are located. Due to the likelihood of strong after shocks and the high vulnerability of these structures, the authorities first asked for a generalized seismic retrofit after the strong shakings of May 20th. In order to accelerate community recovery, this requirement was later loosened, leaving out the buildings which had undergone a strong enough shaking without any damage; the strong enough shaking was defined with reference to the ultimate limit state design earthquake. To the authors’ knowledge, it is the first time that the information on the earthquake intensity and structural damage is used for such a large scale post earthquake simplified safety assessment. In short, the earthquake was used as large experimental test. This paper shows the details of the models and computations made to identify the industrial buildings which have been considered earthquake tested and therefore not compelled to mandatory seismic retrofit. Since earthquake indirect (e.g. due to economic halt) costs may be as large the direct ones, or even larger, it is believed that this method may considerably lower the earthquake total costs and speed up the social and economic recovery of a community.

Experimental studies of scale effects on the shear behaviour of rock joints

Abstract: The effect of scale on the shear behaviour of joints is studied by performing direct shear tests on different sized replicas cast from various natural joint surfaces. The result show significant scale effects on both the shear strength and deformation characteristics. Scale effects are more pronounced in the case of rough, undulating joint types, whereas they are virtually absent for planar joints. The key factor is the involvement of different asperity sizes in controlling the peak behaviour of different lengths of joints. It is shown that as a results both the joint roughness coefficient (JRC) and the joint compression strength (JCS) reduce with increasing scale. The behaviour of multiple jointed masses with different joint spacing is also considered. It is found that despite unchanged roughness, jointed masses consisting of many small blocks have higher peak shear strength than jointed masses with larger joint spacing. These scale effects are related to the changing stiffness of a rock mass as the block size or joint spacing increases or decreases. Economic methods for obtaining scale-free estimates of shear strength are described.

Seismic Hazard Assessment (2003–2009) for the Italian Building Code

Abstract: This paper describes the probabilistic assessment of seismic hazard (PSHA) of Italy in view of the building codes from 2003 to 2009. A code was issued in 2003 as a Prime Minister Ordinance, requiring that a PSHA for updating the seismic zoning would be performed in one year, in terms of horizontal peak ground acceleration (PGA) with 10% probability of exceedance in 50 years on hard ground. For the first time in Italy, a working group, established by the Istituto Nazionale di Geofisica e Vulcanologia, adopted a logic-tree approach to model the epistemic uncertainty in the completeness of the earthquake catalog, the assessment of the seismicity rates and M max, and the ground-motion prediction equations. The seismic hazard has been computed over a grid of more than 16,000 points for the median value (fiftieth percentile) and the eighty-fourth and sixteenth percentiles of the 16 branches of the logic tree. Using the same input model, PGA values and spectral accelerations for 10 spectral periods were computed for nine different probabilities of exceedance in 50 years. This wealth of data made it possible to base the design spectra of a new building code on point hazard data instead of being related to just four zones. The 2009 M w 6.3 L’Aquila earthquake has led many to attempt to test the reliability of this study. In this paper, we analyze suggestions coming from that event and conclude that significant changes to the design spectra are not to be recommended based just on evidence from the L’Aquila earthquake.

Seismic Analysis of Precast Concrete Bridge Columns Connected with Grouted Splice Sleeve Connectors

Abstract: Reinforcing bar couplers are used in prefabricated bridge elements and bridge systems for accelerated bridge construction. Grouted splice sleeve connectors are used in bridge substructures because of the enhanced construction tolerances they offer. This paper presents a simplified modeling strategy for seismic assessment of precast bridge columns connected to precast footings using grouted splice sleeve connectors. A computational model was developed and validated using three half-scale bridge subassemblies tested to failure. Cyclic quasi-static loading was applied to two precast subassemblies and one cast-in-place specimen. The connectors were located in the footing, for the first precast alternative, and in the column end for the second precast alternative along with debonding of reinforcing bars in the footing. Force-based beam-column elements with fiber sections were used to construct the computational model based on plastic hinge weighted integration; the model included low-cycle fatigue and ...