Survey on non-linear cyclic responses of Unreinforced Masonry buildings by means of commercial finite-element codes

This work presents a comparison about the nonlinear cyclic response of unreinforced masonry structures obtained by using commercial calculation codes and on the base of the type of modeling approaches currently available. In particular, several elastoplastic modeling methodologies are considered, representative of a good part of the state of the art for this type of construction: mechanical-based concentrated plasticity macro-element (Tremuri), macro-element with diffuse fiber-based plasticity for flexure and concentrated springs for shear (SeismoStruct) and macro-element with phenomenological-based concentrated plasticity (NextFEM Designer). The purpose of the present research is to evaluate the ability of the different codes to represent the proper hysteretic response of masonry structures. To this aim, several experimental tests from literature are analyzed and compared; two different masonry panels, characterized by different resistant mechanisms, and an entire perforated wall have been studied through nonlinear cyclic static analyses. The reported comparison, mainly focused on the numerical cyclic behaviour exhibited by each computer program, is conducted on the basis of the path of the cycles obtained and on the amount of dissipated energy

Review of experimental cyclic tests on unreinforced and strengthened masonry spandrels and numerical modelling of their cyclic behaviour

A reliable numerical modelling for the cyclic behaviour of unreinforced and strengthened masonry spandrels is herein presented. The proposed numerical model is adapted from Tomazevic-Lutman\u2019s model for masonry piers in shear and it has been validated upon an experimental campaign conducted at Department of Engineering and Architecture of University of Trieste. The tests were conducted on Hshaped full-scale specimens imposing vertical displacements of increasing amplitude on one leg. Four unreinforced masonry specimens arranged with different masonry material (bricks and stones) and lintel supports (wooden lintel, masonry arch) were considered. Each specimen was then reinforced with a different strengthening technique (tensioned bars, steel profiles, CFRP laminates) and re-tested. Analytical relationships were proposed, based on those available in some Codes of Practice, to estimate the maximum shear resistance of URM and RM spandrels. These relationships provide resistance values in good agreement with the experimental results and can be correctly employed to define the cyclic model of the spandrel to be used in the numerical simulation. The cyclic shear-displacement curves obtained through the numerical model are in good agreement with those of the experimental tests and very good assessment of the dissipated energy was obtained

Seismic assessment of a heavy-timber frame structure with ring-doweled moment-resisting connections

The performance of heavy-timber structures in earthquakes depends strongly on the inelastic behavior of the mechanical connections. Nevertheless, the nonlinear behavior of timber structures is only considered in the design phase indirectly through the use of an R-factor or a q-factor, which reduces the seismic elastic response spectrum. To improve the estimation of this, the seismic performance of a three-story building designed with ring-doweled moment resisting connections is analyzed here. Connections and members were designed to fulfill the seismic detailing requirements present in Eurocode 5 and Eurocode 8 for high ductility class structures. The performance of the structure is evaluated through a probabilistic approach, which accounts for uncertainties in mechanical properties of members and connections. Nonlinear static analyses and multi-record incremental dynamic analyses were performed to characterize the q-factor and develop fragility curves for different damage levels. The results indicate that the detailing requirements of Eurocode 5 and Eurocode 8 are sufficient to achieve the required performance, even though they also indicate that these requirements may be optimized to achieve more cost-effective connections and members. From the obtained fragility curves, it was verified that neglecting modeling uncertainties may lead to overestimation of the collapse capacity

A novel method for non-linear design of CLT wall systems

Inthis paper,a non-linear procedure for the seismic design of metal connections in cross-laminated timber (CLT) walls subjected to bending and axial force is presented. Timber is conservatively modelled as an elasto-brittle material, whereas metal connections (hold-downs and angle brackets) are modelled withan elasto-plastic behavior. The reaction force in each connection is iteratively calculated by varyingthe position of the neutral axis at the base of the wall using a simple algorithm that was implemented\ufb01rst in a purposely developed spreadsheet, and then into a purposely developed software. This methodis based on the evaluation of \ufb01ve different failure mechanisms at ultimate limit state, starting from the fully tensioned wall to the fully compressed one,similarly to reinforced concrete (RC) section design.By setting the mechanical properties of timber and metal connections and the geometry of the CLT panel, the algorithm calculates, for every axial load value, the ultimate resisting moment of the entire wall and the position of the neutral axis. The procedure mainly applies to platform-type structures with hold-downs and angle brackets connections at the base of the wall and rocking mechanism as the prevalentway of dissipation. This method allows the designer to have information on the rocking capacity of thesystem and on the failure mechanism for a given distribution of external loads. The proposed methodwas validated on the results of FE analyses using SAP2000 and ABAQUS showing acceptable accuracy

A macro-model with nonlinear springs for seismic analysis of URM buildings

Seismic assessment of existing unreinforced masonry buildings represents a current challenge in structural engineering. Many historical masonry buildings in earthquake regions were not designed to withstand seismic loading; thus, these structures often do not meet the basic safety requirements recommended by current seismic codes and need to be strengthened considering the results from realistic structural analysis. This paper presents an efficient modelling strategy for representing the nonlinear response of unreinforced masonry components under in-plane cyclic loading, which can be used for practical and accurate seismic assessment ofmasonry buildings. According to the proposed strategy, generic masonry perforated walls are modelled using an equivalent frame approach, where each masonry component is described utilising multi-spring nonlinear elements connected by rigid links. When modelling piers and spandrels, nonlinear springs are placed at the two ends of the masonry element for describing the flexural behaviour and in the middle for representing the response in shear. Specific hysteretic rules allowing for degradation of stiffness and strength are then used for modelling the member response under cyclic loading. The accuracy and the significant potential of the proposed modelling approach are shown in several numerical examples, including comparisons against experimental results and the nonlinear dynamic analysis of a building structure

A component approach for non-linear behavior of cross-laminated solid timber panels

Many possible emergency conditions, including evacuations, negatively affect the urban transportation system by substantially increasing the travel demand and/or reducing the supplied capacity. A transportation model can be used to quantify and understand the impact of the underlying disasters and corresponding management strategies. To this end, we develop an efficient methodology suitable for simulating multimodal transportation systems affected by emergencies, based on the novel integration of an activity-based choice model with both pre-trip and en-route choices, and a macroscopic or mesoscopic dynamic network loading model. The model structure first estimates the daily equilibrium and then uses that result as a starting point to simulate the emergency situation without further iterations. Unlike previous efforts, our methodology satisfies all requirements identified from literature regarding transportation modeling for emergencies, and is sufficiently general to investigate a wide range of emergency situations and management strategies. An evacuation case study for Delft shows the feasibility of applying the methodology. Furthermore, it yields practical insights for urban evacuation planning that stem from complex system dynamics, such as important interactions among travel directions and among modes. This supports the need for a comprehensive modeling methodology such as the one we present in this paper