Publications

Seismic Retrofit of a URM Building with Timber-Based Coating: A Numeric Study

Retrofitting of Traditional Timber Floors

Seismic out-of-plane repair and strengthening of masonry infill walls using timber strong-backs

Seismic retrofit of masonry walls using timber strong-backs

A high proportion of New Zealand's clay brick unreinforced masonry (URM) structures have not been retrofitted to resist earthquake forces, and in particular to prevent out-of-plane failures which are the most critical deficiencies of URM buildings. Despite a number of seismic improvement techniques having been applied previously there is a significant lack of experimentally validated simple and cost-effective solutions that also consider the impact on the building tenants, aesthetics and heritage building fabric. The main objectives of the research presented herein were to develop and validate seismic securing techniques for URM solid- and cavity-walls that satisfied the above conditions. Full-scale shake-table testing of two cavity and three double-leaf solid clay brick URM walls was undertaken. The vertical timber framing that is typically considered to be a non-structural support for the inner wall lining was used as part of the retrofit solution and was fixed to the wall using mechanical screw-ties in order to form a strong-back. The intended outcomes of the research reported herein included (i) measuring via laboratory testing the improvement of seismic capacity in terms of peak ground acceleration (PGA) achieved and maximum out-of-plane displacement experienced by the URM solid- or cavity-walls due to strong-back retrofit installation; (ii) comparing the performance of different strong-back configurations; (iii) providing construction details, and providing analytical formulations for response prediction.

ANALYSIS OF EXPERIMENTAL RESULTS ON A CHEMICAL-MECHANICAL CONNECTION IN TIMBER CONCRETE COMPOSITE FLOORS

A new type of connection is presented for timber to concrete composite structures, using new glued laminated timber beams. The connection comprises a particular milling to create back-to-back L-shaped longitudinal grooves within the top side of the glulam joist with a number of wood tenons, and the concrete slab. The connection is prepared by using also a high resistance anti-shrink cement mortar which bonds to the timber (giving the chemical connection), with steel reinforcing bar trusses anchored in the mortar and protruding into the concrete to give the mechanical connection. The efficacy and validity of the system are demonstrated by a comprehensive experimental and numerical investigation, which allowed also the determination of the stiffness of the composite beam and its load carrying capacity. The research has been carried out in two phases; initially, several solutions have been studied, while in the second phase the most interesting one has been analysed in detail and optimized. An accurate numerical model has also been implemented with the aim of correctly predicting the mechanical behaviour of this particular type of connection to be used for new timber-concrete composite structures.

A NOVEL HYBRID WOODEN STRUCTURAL SYSTEM FOR MULTI-STOREY BUILDINGS IN SEISMIC PRONE AREAS

The development of innovative engineered wood products has greatly increased the possibility of using timber as structural material, opening new markets in the construction sectors, such as multi-storey residential and collective (e.g., schools) buildings. The use of timber structures is in fact still confined to low- and mid-rise buildings. The HyWood4Buildings project aims to overcome the existing constraints in the timber construction sector, proposing a novel hybrid structural system for taller timber buildings. This system combines two distinct but interacting components: a modular hybrid steel-timber lateral load resisting (HyST-LaR) system and a solid-sawn wall (SoN-Wall) system. This paper presents the structural characterization of the innovative HyST-LaR system through an experimental campaign at component-level and numerical analysis with a first glance to the development of an analytical model.

In-plane repair and strengthening of rubble stone masonry with single-sided natural hydraulic lime fabric reinforced mortar

Composite reinforced mortar (CRM) systems represent a strengthening solution for existing masonry structures consisting of a composite mesh embedded within a layer of structural mortar. Diagonal compression tests on natural stone masonry panels (URM) are reported, aimed at assessing the effectiveness of a hybrid CRM-FRCM system. The tested system was comprised of a 25 mm natural hydraulic lime-based mortar and a 20 × 20 mm AR glass grid applied on only one side of the panels in order to simulate the most commonly encountered strengthening configuration. The results showed an average increase in shear resistance of 32% compared to the average properties of the URM walls, while preserving the average shear stiffness. In addition, previously tested natural stone URM panels were repaired using the same strengthening solutions and were retested in diagonal compression. For the retested specimens the original shear capacity was recovered up to 98%, demonstrating the effectiveness of the strengthening system as a remediation solution for damaged masonry.

Comparison of <i>In Situ</i> and Laboratory Testing for the Characterization of Old Timber Beams before and after Intervention

In this paper an investigation campaign, carried out in occasion of the restoration of a timber floor in the Belasi Castle (Trentino, Italy), is reported. In order to validate a testing procedure for the calibration and control of an innovative wood-wood strengthening technique, results of tests performed in situ on the structural elements, in both the original and the repaired condition, have been compared with those obtained in laboratory on some dismantled beams. For the characterization of the material decay, both local mechanical and global vibrational testing have been carried out. For the mechanical characterization of the beams, before and after repair, direct static bending tests have been performed, with distributed loads, on site, and according to standard four-points loading schemes, in laboratory.

Effect of boundary conditions and other factors on URM wall out-of-plane behaviour: Design demands, predicted capacity, and in situ proof test results

Testing of URM wall-to-diaphragm through-bolt plate anchor connections

The presence of effective wall-to-diaphragm connections has been shown to significantly improve the global seismic behavior of unreinforced masonry (URM) buildings. However, despite the importance of such connections, there remains a paucity of experimental research to provide physical validation of current recommendations in design standards and guidelines. The experimental study reported herein included a total of 18 tests which were undertaken in two phases, with Phase 1 testing being undertaken on existing vintage plate anchor connections in an existing URM building and Phase 2 testing involving newly installed plate anchor connections in two additional existing URM buildings. The tested buildings offered variation in material properties, levels of axial load, and wall thickness as test parameters. Attained failure modes and corresponding force-displacement curves are presented herein, as well as comparisons regarding the influence of varying test parameters on the ultimate pull-out capacity. Prediction of plate anchor capacity was undertaken using a basic mechanics approach, and comparisons to current strength recommendations in standards and guidelines are provided.

Experimental and numerical evaluation of geometrical imperfection effects on the load bearing capacity of small-scaled voussoir arches

The study of the behaviour of masonry arches represents a complex problem, which involves different aspects that can significantly affect the load bearing capacity of such structures. In this regard, geometrical imperfections, such as the irregular shape of the arch blocks, the initial position of the first and last voussoirs (boundary conditions), the alignment between the adjoining blocks and the rounded corners of each block, play an important role. An experimental campaign was conducted on a toy arch made by eleven irregular blocks, with the aim of evaluating the effect of such irregularities. A numerical model was developed basing on lower bound (LB) and upper bound (UB) limit analysis approaches (referred to as the static and the kinematic theorem, respectively). A linear programming (LP) solving algorithm was implemented in the software MATLAB and used to solve the minimization/maximization problems. The probability distribution of each considered nonlinearity was estimated, the results of the numerical analysis were correlated with the experimental outcomes and a Montecarlo simulation was carried out to validate the hypothesised probability distributions.

A simplified analytical approach for CLT-based seismic retrofit of existing reinforced concrete structures

Comparison between predicted URM wall out-of-plane strength based capacity and in situ proof test results

Unreinforced masonry (URM) building construction is prominent in the form of load-bearing, partition, and infill walls. Significant out-of-plane (OOP) failures of URM walls often occur during moderate and severe earthquake shaking and such walls are often identified in structural engineering assessments as being amongst the most vulnerable elements to OOP demands, especially earthquakes. For undamaged, in situ wall conditions where material properties are known and boundary conditions reflect idealised conditions assumed in analytical predictive models, these predictive models are easily applied, although the accuracy of the model outputs may still not be well understood. Furthermore, when in situ conditions do not reflect idealised conditions assumed in analytical predictive models, engineers are often uncertain as to which analytical models and inputs are most appropriately applied. Hence, an analytical campaign was undertaken to provide specific examples for structural engineering practitioners assessing the OOP seismic behaviour of URM walls, and the predictive results reported herein were compared to previously reported experimental results of eighteen tests on existing URM walls performed in situ. The considered wall configurations represented a variety of geometries, boundary conditions, pre-test damage states, and material properties. The average ratio and associated coefficient of variation (CV) of predicted strengths to measured strengths were determined to be 0.84 (CV 0.56) and 0.93 (CV 0.25) for the unbounded and bounded wall conditions, respectively, and corresponding recommendations for analytical assessment were made for practicing engineers.

Tension and shear anchorage systems for limestone structures

Editorial

An Integrated Approach to Improve Seismic and Energetic Behaviour of RC Framed Buildings Using Timber Panels

In the present paper, an integrated intervention system applicable to concrete-framed buildings is presented. The purpose of the intervention is to improve both the seismic and the energetic behaviour of such buildings using cross-laminated timber (CLT) panels. Two alternative intervention configurations with different levels of invasiveness are described. Considering a double-wythe masonry-infilled frame, the most invasive configuration consists in the replacement of the external masonry wythe with the CLT panel, while the least invasive configuration consists in the arrangement of the CLT panel from the outside without removing the wythes. The technical details and implementation procedures were studied, considering functionality and disturbance to occupants. An isolated one-storey-one-bay frame was used as a reference for the seismic and thermal analyses. Subsequently, the two intervention configurations were applied to a case-study building by identifying two alternative intervention strategies. The obtained results showed that the proposed integrated intervention approach can significantly reduce both the seismic vulnerability and the energy consumption of concrete buildings.

Analytical, numerical and experimental assessment of vibration performance in timber floors

Seismic Out-of-Plane Retrofit of URM Walls Using Timber Strong-Backs

The susceptibility of unreinforced masonry (URM) walls to collapse under seismic loading has been repeatedly observed and documented across a multitude of earthquakes worldwide. The out-of-plane failure of walls is commonly the critical failure mechanism for URM structures and poses a significant risk to life. Despite various seismic improvement techniques being applied previously there is a significant lack of experimentally validated simple and cost-effective solutions that also consider the impact on the building tenants, building aesthetics, and heritage fabric of the structure. Such retrofits are needed to facilitate the preservation of the URM building stock and to ensure the safety of those who work and live in and around these structures. The retrofit technique studied herein consisted of connecting vertical timber elements (strong-backs), to the interior surface of a building’s walls using mechanical anchors. Non-structural timber framing commonly exists to support the inner wall lining of URM buildings and its use, as a part of the retrofit, results in a cost effective and low impact solution. The out-of-plane behavior of as-built and retrofitted masonry walls was investigated by conducting full scale semi-static cyclic airbag tests. The outcomes of this testing regime include (i) quantification of improvement in seismic capacity and out-of-plane displacement capacity and (ii) comparison of the performance using different strong-back configurations.

Numerical Modeling Strategies for In-Plane Behavior of Straight Sheathed Timber Diaphragms

Two modeling approaches with different levels of refinement were used to numerically investigate the influence of different parameters on the response of straight sheathed timber diaphragms when subjected to in-plane loading. The investigated parameters included diaphragm aspect ratio, scale factor (i.e., diaphragm size), impact of board-to-board contact phenomena, and the effects of board-to-board shear force exchange. The aim of the work presented herein was to use numerical modeling to investigate the aspects that potentially contribute to the difference in experimental behavior reported in literature and that consequently might have influenced provisions encompassed in the most recent standards for the assessment of timber diaphragms. The modeling strategies were validated against a wide range of available experimental data on newly constructed and vintage timber floor specimens. Analysis results confirmed that the in-plane behavior of straight sheathed diaphragms is significantly influenced by parameters that are often neglected by numerical studies and assessment procedures.