Ario Ceccotti

New Technologies for Construction of Medium-Rise Buildings in Seismic Regions: The XLAM Case

This paper reports on the outcomes of an experimental test performed on a full-scale building constructed using innovative technology. The experimental results are compared with the outcomes of a numerical analysis with the aim to derive the behaviour factor q used in a simplified elastic design of the building under seismic actions.

Cyclic Behavior of CLT Wall Systems: Experimental Tests and Analytical Prediction Models

AbstractAn experimental program was performed at IVALSA Trees and Timber Institute on single and coupled cross-laminated (CLT) wall panels with different anchoring systems and different types of joints between adjacent panels. The mechanical properties of CLT walls were assessed and are critically discussed in the paper. The connector layout and the design of the screwed vertical joints were found to markedly affect the overall behavior of the structural system. The in-plane deformations of CLT panels were almost negligible, whereas concentration of forces and deformations mainly occurred in the connections. Advanced analytical models for nonlinear pushover analysis of CLT wall systems were developed and verified against test results. The models take into account all stiffness and strength components of connectors, as well as the bending and shear deformation of the panels. A parametric study of CLT wall systems with different aspect ratios and wall segmentation was performed, showing that segmentation of...

Cyclic behavior of typical screwed connections for cross-laminated (CLT) structures

This paper presents the results of an extensive experimental programme on typical cross-laminated timber (CLT) screwed connections conducted at CNR-IVALSA research institute. In-plane monotonic and cyclic shear and withdrawal tests were performed on screwed wall-to-wall, floor-to-floor and wall-to-floor CLT connections. Mechanical properties such as strength, stiffness, energy dissipation, ductility ratio and impairment of strength were evaluated. The experimental results showed good performance of CLT screwed joints under cyclic loads when ductile behaviour was achieved. Brittle response occurred only in cases where requirements for end and edge distances were not satisfied. The experimental characteristic shear strength and mean slip modulus of the connections were compared with values obtained using analytical design equations. The Eurocode 5 (EC5) formulas overestimated the characteristic strength values in some cases, while the Uibel and Blaß formulas specifically developed for CLT connections provided more accurate and conservative predictions. In cases where brittle failures were attained, the analytical values overestimated the experimental ones. This issue can be avoided when the requirements for minimum edge and end distances stated by EC5 are fulfilled. EC5 empirical formulas for the prediction of the screw connection slip modulus at serviceability limit state corresponded well with the experimental elastic values. The overstrength factor, which is of great importance in capacity-based design, was also evaluated, and a conservative value of 1.6 can be recommended for screwed CLT connections.

Fire Resistance of Cross-Laminated Timber Panels Loaded Out of Plane

AbstractThis paper describes bending tests at ambient temperature and large-scale fire tests of cross-laminated timber (Xlam) floor panels. Three specimens exposed to standard fire curve were loaded out-of-plane with different levels of uniformly distributed load, and in two cases collapse was reached. Other unloaded panels were protected using different cladding systems with the aim to investigate their thermal behavior. Experimental data obtained from the tests and discussed within the paper includes modulus of elasticity and bending strength at ambient temperature, temperature distribution, charring depth, charring rate, residual cross section, midspan deflection, and time to failure in fire conditions. This data was compared with numerical results obtained by implementing a finite-element model in Abaqus software package for sequential thermal and structural analyses, demonstrating the accuracy of the model. The overall fire performance of the Xlam panels was satisfactory; times to failure of 99 and 1...

Concrete-Plated Wooden Shear Walls: Structural Details, Testing, and Seismic Characterization

AbstractThis paper discusses the structural characterization of a novel hybrid shear-wall system formed by coupling standard platform-frame panels with an external reinforced concrete shelter formed of precast slabs screwed to the wooden frames. The external RC skin is intended as a supplementary bracing system, increasing strength and dissipative capacity of the bare timber frame. The structural performance of such hybrid shear wall under monotonic and cyclic loading was first theorized analytically on the basis of code provisions and then confirmed via experimental tests. The novel shear walls demonstrated to fulfill the requirements prescribed by Eurocode 8. In particular, the analyzed system belongs to high ductility class (HDC). Finally the seismic response of a reference building realized with the innovative hybrid shear walls was simulated by means of a numerical model validated on experimental tests; the suitable behavior factor for the building was estimated.

Behaviour of Cross-Laminated Timber Panels under Cyclic Loads

In this paper, the behaviour of cross-lam (CLT) wall systems under cyclic loads is examined. Experimental investigations of single walls and adjacent wall panels (coupled walls) in terms of cyclic behaviour under lateral loading carried out in Italy at IVALSA Trees and Timber Institute and in Canada at FPInnovations are presented. Different classifications of the global behaviour of CLT wall systems are introduced. Typical failure mechanisms are discussed and provisions for a proper CLT wall seismic design are given. The influences of different types of global behaviour on mechanical properties and energy dissipation of the CLT wall systems are critically discussed. The outcomes of this experimental study provides better understanding of the seismic behaviour and energy dissipation capacities of CLT wall systems.

Application of a Translational Tuned Mass Damper Designed by Means of Genetic Algorithms on a Multistory Cross-Laminated Timber Building

AbstractThis paper presents a numerical study conducted on a seven-story timber building made of cross-laminated (X-lam) panels, equipped with a linear translational tuned mass damper (TMD). The TMD is placed on the top of the building as a technique for reducing the notoriously high drifts and seismic accelerations of these types of structures. TMD parameters (mass, stiffness, and damping) were designed using a genetic algorithm (GA) technique by optimizing the structural response under seven recorded earthquake ground motions compatible, on average, with a predefined elastic spectrum. Time-history dynamic analyses were carried out on a simplified two-degree-of-freedom system equivalent to the multistory building, while a detailed model of the entire building using two-dimensional elastic shell elements and elastic springs for modeling connections was used as a verification of the evaluated solution. Several comparisons between the response of the structure with and without TMD subjected to medium- and h...

A Proposal for a Procedure to Evaluate the Seismic Vulnerability of Historic Timber Frame Buildings

The seismic vulnerability of historic timber frame building heritage is difficult to quantify in retrospect. However, in order to maintain, restore or even retrofit these buildings, it is indispensable not only to understand their performance under an earthquake loading, but also to gain quantitative information on stiffness, load bearing capacities and failure modes of the used timber frame technique. A possibility to assess earthquake behaviour is full-scale testing, but this is very expensive and it is nearly impossible to cover all the different timber frame systems, the variations between the different systems and different earthquake loadings. Therefore, small-scale tests on components or substructures are more suitable whose outcomes can be used for nonlinear dynamic modelling of buildings. This contribution proposes a simple testing-modelling approach to quantify the seismic vulnerability of timber frame buildings. The testing includes monotonic and quasi-static reversed cyclic tests on shear walls which are re-built specimens mirroring as exactly as possible the historic archetypes for both wall dimensions and used materials. The test results are then used to develop nonlinear dynamic lumped mass models which are subjected to various earthquake accelerograms. By increasing the single earthquake’s peak ground acceleration (PGA) values, the seismic performance of the investigated historic structure can be evaluated and suggestions can be given with respect to restoring or retrofitting measures. On the basis of a valid and reliable mathematical model, also parameter studies varying, for instance, the number of fasteners in joints are more readily carried out than with experimental methods.

Seismic Vulnerability of Borbone Masonry Reinforced with Timber Frames

After the 1783 earthquake, under the Borbone kingdom, new building regulations were introduced in the Calabria region (Italy) with the main scope of reducing the seismic vulnerability of the building asset in these highly seismic areas. The Borbone system consisted of masonry walls reinforced with timber frames and prescribed a symmetrical development in plan and elevation as well as height limitations. These measures aimed at increasing the seismic resistance of buildings and hence, in general, at reducing the socio-economic impact of future seismic events. In order to maintain, repair or retrofit these buildings, it is indispensable not only to understand their qualitative performance under an earthquake loading, but also to gain quantitative information on stiffness, load bearing and energy dissipation capacity and failure modes. This paper presents first investigations on the seismic vulnerability of simple Borbone structures where modelling assumptions such regularity in plan and elevation hold and only one shear wall system was used. Re-built shear wall specimens mirroring as exactly as possible a wall of the Palazzo Vescovile in Mileto (Italy), built according to the Borbone Istruzioni after the 1783 earthquake, were tested under quasi-static cyclic in-plane loading. By means of these tests, lateral properties and damage patterns of Borbone shear walls under horizontal loading were assessed and, even if limited to a single panel, earthquake behaviour patterns were evaluated. The test results on the shear walls in terms of hysteretic loops were used to develop a non-linear dynamic lumped mass model of a case study Borbone building which was subjected to various earthquake accelerograms. The single earthquake’s peak ground acceleration (PGA) values were increased until a previously defined near-collapse state in terms of maximum interstorey drift of the modelled building was reached. The thus obtained ultimate values for the PGA represent the sustainable level of seismic action of the investigated Borbone structure and ranged from 0.25g (North American earthquake) up to 1.52g. The effectivity of Borbone building regulations could be shown.

Innovative timber building systems: comparative testing and modelling of earthquake behaviour

Several innovative timber building systems were developed in the past few years, among which dowel-laminated timber, CLT with interspaces and prefabricated timber wall elements, whose design requires also verification of the lateral load-carrying system. Therefore, shear wall tests on these three building systems were carried out. Timber frame shear walls were also tested to compare load–displacement behaviour, failure modes and energy dissipation capacity. The four investigated systems exhibit similar shapes for load–displacement curves albeit reaching different stiffness and capacity values. Based on the test results, 2D models of shear walls and a case study building were developed in order to investigate the seismic behaviour of the discussed timber building systems. The hysteretic behaviour of the shear walls and of the case study building was assigned to non-linear hysteretic springs. The building models were then subject to accelerograms whose intensities were increased until the near-collapse state was reached. Via these nonlinear dynamic simulations in the time domain, design behaviour factors valid for force-based seismic design were established. Based only on a few common tests on shear walls, a general statement regarding the seismic behaviour of novel systems can be given using this procedure. The three investigated innovative timber building systems proved to be suitable for the use in seismic active areas and can cover the same application range as conventional timber frame buildings.