We investigate on the strength and ductility properties of recycled PET fiber-reinforced concretes (RPETFRCs) showing different mix-designs and PET filaments with variable mechanical and geometric properties. Available literature results of compression tests and four-point bending tests on such materials are reviewed comparing laboratory results in terms of compressive strength, first crack strength and ductility indices. The examined tests highlight that most relevant effects of the recycled PET fiber reinforcement are concerned with material toughness and ductility. In the case of low-strength concretes, significant compression and flexural strength enhancements due to the addition of recycled PET fibers are also observed.
Uncategorized
GIULIO PIZZETTI AND THE STRUCTURES IN ARCHITECTURE
Please note that this paper is available only in Italian
DESIGN OF HYSTERETIC DAMPED BRACES TO IMPROVE THE SEISMIC PERFORMANCE OF STEEL AND R.C. FRAMED STRUCTURES
A Displacement-Based Design (D.B.D.) procedure is adopted for the retrofit of framed structures by inserting hysteretic damped braces (HYDBs) in order to attain, for a specific level of seismic intensity, a designated performance level. To check the reliability of the design procedure, two six-storey buildings are considered as having steel and r.c. framed structures, which, originally designed in a medium-risk seismic region, have to be retrofitted as if in a high-risk seismic region. To avoid high deformability of the steel structure at the damage limit state (SLD) and brittle behaviour of the r.c. structure at the life-safety limit state (SLV), two retrofitting structural solutions are examined: additional diagonal braces; HYDs supported by the additional diagonal braces. Nonlinear dynamic analyses under real ground motions are carried out by a step-by-step procedure. The frame members and the HYDs are idealized by a bilinear model; an elastic behaviour is considered for the braces.
MULTIAXIAL PRESTRESS OF REINFORCED CONCRETE I-BEAMS
We analyze the effects of multiaxial prestress on the limit behavior of I-shaped reinforced concrete elements subjected to combined axial load and bending. We provide a collection of design charts and moment – curvature diagrams for reinforced concrete I-beams with laterally and longitudinally prestressed flanges. The given results highlight the special ability of the active prestress technique in enhancing the strength and ductility properties of seismic resistant columns and shear walls.
DYNAMIC BEHAVIOUR OF CRACKED GRANITE AND MARBLE COLUMNS RETROFITTED WITH STEEL COLLARS
Marble and heavy stone columns are widely diffused in ancient churches and historical buildings in all the Mediterranean area. Their good mechanical properties allowed carrying great load values, while their bright colours and aesthetical characteristics have been used by a lot of ancient architects to achieve structural solutions with great visual impact.
Despite their good compressive strength, marble columns could be damaged from environmental effects (e.g. long- term effects or thermal loads), which could crack the structural members. In this way, the slenderness of the column increases drastically and the presence of an imposed ground shaking could be critical, since the column will be more vulnerable to rocking motion and to overturning risk.
This paper focuses on the rocking behaviour of cracked granite and marble columns subjected to a pulse type ground shaking. The effect of the presence of circular collars is analysed by means of a mechanical model. The overturning spectra are determined including the presence of the collars, showing their efficiency in reducing the overturning risk. Comparisons are shown with numerical analyses and a simplified design method is proposed.
STRUCTURAL CAPACITY OF MASONRY WALLS UNDER HORIZONTAL LOADS
In the present work we describe a procedure for determining the ground acceleration that activates the in-plane mechanism of a wall panel with openings. The method, based on the assumption that the material is unilateral (namely a No-Tension material in the sense of Heyman), leans on the kinematic theorem of limit analysis. By working with the kinematic theorem, we admit singular strains representing concentrated fractures; in other words we allow for strong discontinuities in the displacements. In recent papers we adopted finite elements with strong discontinuities and search for local minima of the energy (in proximity of equilibrium trajectories) by minimizing the energy through descent, both with respect to the displacements and with respect to the position of the jump set. In this paper we propose a similar, though simplified, strategy to explore compatible mechanisms having free discontinuities. The numerical implementation of the proposed approach is discussed through illustrative examples, on examining collapse mechanisms of masonry structures subject to vertical and seismic loads.
NUMERICAL FRAMEWORK FOR NONLINEAR ANALYSIS OF TWO-DIMENSIONAL LIGHT-FRAME WOOD STRUCTURES
This paper presents and assesses a new numerical framework for the nonlinear, inelastic analysis of two-dimensional (2D) vertical wood building systems that incorporate sheathed light-frame wood shear walls as seismic force-resisting system. The 2D building model is based on a sub-structuring approach that considers each floor diaphragm as a rigid body with three kinematic degrees-of-freedom (DOF). Each inter-storey shear wall assembly, including the floor diaphragms above and below, can then be simulated by a six-DOF sub-structure element with internal nonlinear DOF. The shear wall element takes into account deformations in the framing members, contact/ separation phenomena between framing members and diaphragms, anchoring equipment such as anchor bolts and hold-downs and all sheathing-to-framing connections. Corotational descriptions are used to solve for displacement fields that satisfy the equilibrium equations in the deformed configuration, accounting for geometric nonlinearity and P-Δ effects. To appraise the proposed numerical framework, the predictions of the numerical model are compared to experimental results from single and two-storey full-scale shear wall specimens. These examples demonstrate the capability of the numerical framework to simulate accurate load paths in the shear wall assemblies and successfully predict variations in strength, stiffness and energy dissipation characteristics of the seismic force-resisting system.
SEISMIC DESIGN OF MULTI-STOREY CROSS LAMINATED TIMBER BUILDINGS ACCORDING TO EUROCODE 8
Cross Laminated Timber (CLT) structures are nowadays increasingly used worldwide and mostly in Europe where the system originated. However, in spite of this diffusion which led to the construction of a great number of multi-storey buildings all over Europe, still Eurocodes are almost completely missing provisions for CLT designers, especially regarding the seismic design. Nevertheless, Eurocode 8 requires in most cases, due to the regularity criteria being not fulfilled for most of the buildings, the use of the modal response spectrum analysis method, i.e. the linear dynamic analysis. This method requires the correct estimation of the lateral stiffness of the building in order to accurately calculate the design seismic forces in the building, which may be significantly underestimated or overestimated depending on the size of the building and the shape of the design spectrum. This can be done by modelling each connection with different methods that are often based on available test results, which are not easily accessible by a practicing engineer. This paper provides a design approach for dynamic linear modelling of CLT structures using SAP 2000. Equations are proposed based on available design codes and literature references, and used to design a 3-storey case study building. Further provisions for the seismic design of CLT buildings which are not included in Eurocode 8 are also given. Finally, the proposed design model is also compared with the results of the shaking table tests conducted in 2006 in Japan by CNR-IVALSA on a three-storey CLT building.