Thierry Descamps

Structural Characterization and Numerical Modeling of Historic Quincha Walls

ABSTRACT Quincha is a construction technique found in upper stories of many historic residential buildings on the coast of Peru, consisting of a timber frame with a woven cane and mud infill. This article presents the methodology for the development of a numerical model of the quincha system. The quincha walls have been subdivided into three components, the timber frame, bracing, and infill, and the modeling of each component is calibrated separately using experimental and analytical techniques. The resulting numerical model is found to successfully reproduce the behaviour of test specimens. The developed model can be used to assess the global seismic behavior of historic buildings containing quincha of varying geometries. This is demonstrated by modeling a portion of one of the facades of a well-known casona in Lima, Hotel el Comercio.

Single step joint: overview of European standardized approaches and experimentations

In the field of Built Heritage Restoration, engineers have to work with old structures made of poorly preserved timber elements. The assessment of timber elements and connections is a major issue for engineers involved in a restoration project. Before thinking about any intervention techniques, engineers have to properly understand how the carpentry connections fail, which parameters influence the failure modes (e.g. geometry of the joint, mechanical properties of the wood) and how the internal forces are distributed into the joint to finally figure out how to design the traditional carpentry connections. The present paper aims at raising those questions focusing on the Single Step Joint (SSJ) design. Even if this common joint between the rafter and the tie beam is geometrically simple, one may pick up three SSJ families from the past till today: the Geometrical Configuration Ideal Design, the Geometrical Configuration Perpendicular to the Tie Beam and the Geometrical Configuration Perpendicular to the Rafter. The first one is more recent because its geometry requires accurate timber cutting, using new technologies (e.g. Computer Numerical Control). For each one, some general design rules about the SSJ geometrical parameters are defined by some European standards (e.g. Eurocode 5 in Design of timber structures—part 1‐1: general—common rules and rules for buildings. CEN, European Standardisation Institute, Brussels, 8) or authors (e.g. Siem and Jorissen in Shatis’15: 3rd international conference on structural health assessment of timber structure, vol 1. Wroclaw, Poland, 9–11 Sept 2015, 11), but no detail is available on how to design this connection in order to prevent the shear crack at the heel depth in the tie beam, or the compressive crushing at the front-notch surface. Hence the design rules and the emergence of failure modes must be defined according to the SSJ geometrical parameters. In order to check the design equations and the failure modes, lab tests on the three SSJ families have been carried out, modifying the heel depth, the shear length and the inclination of the rafter.

Finite element modelling of inclined screwed timber to timber connections with a large gap between the elements

Since the 80’s, Johanssen’s Yield Theory has been adapted to fit new design practices: fastening of timber elements with a layer of insulation (or gap) between the elements or fastening with inclined fasteners. However no rules exist for connections with large gaps (up to 500 mm) and inclined fasteners. The behaviour of screwed connections (timber/large gap/timber) is modelled using an orthotropic material, cohesive surface, Hill criterion and a fictitious material that wraps the screw and models a complex medium where steel and wood interact. The calibrated FE model is finally compared to experimental results.

Development of a Specific Finite Element for Timber Joint Modeling

Widely used for light frame structures or for heavy laminated wood structures, dowel-type fasteners are the most commonly used kind of connectors in timber construction. The purpose of this work is to develop a tool for the semi-rigid analysis and design of such joints. Firstly, interests and approaches described in literature for the semi-rigid modeling of timber plane frames are summarized. Secondly, for a better understanding of the problem, the main characteristics of wood used as a structural material are presented. Finally, a method for an efficient study of joints built with dowel-type fasteners is proposed and developed. This method consists of the introduction of a specific finite element called “Finite Semi-Rigid Element (FSRE)” between the ends of the jointed members. This joint element consists of two nodes, each with three degrees of freedom. These nodes will be tied with common beamelements during the FE analysis. The stiffness of the FSRE is computed from the geometry of the joints and embedding stiffness of all fasteners, along and perpendicular to the grain. The embedding characteristics of fasteners are defined with help of their experimental load-slip curves (fitted with Foschis models) leading finally to the resolution of a FE non-linear problem.

Refurbishment of existing timber floors with screwed CLT panels

ABSTRACT A well-known, light, and almost reversiblere furbishment solution for existing timber floors is the use of a top timber flange connected to the joists to build up a “new” composite. This article proposes an improvement of that technique by using a cross-laminated timber (CLT) flange connected to the joists with inclined self-tapping screws. The use of an additional gap between the CLT and the existing joists contributes to increase the bending stiffness too. The inner gap is fixed by timber blocks resistant in compression but non-efficient in bending. These blocks act with the inclined screws to behave as a Pratt truss. An analytical model of the refurbishment is presented and a design example is discussed. Different configurations are finally introduced and compared to highlight pros and cons of the technique.

Historic timber roofs modelling: prosthesis and resin repairs

1.1. Structural analysis of old timber frameworks Nowadays, a considerable number of timber structures require structural intervention due to material decay, improper maintenance of the structure, faulty design or construction, lack of reasonable care in handling of the wood, accidental actions or change of use. While the assessment of old timber structures is complex, it is an essential precursor to the design of the reinforcement of the joints. Owing to a lack of knowledge or time, the species and/or grade assumed are often an overly conservative estimate which can lead to unnecessary replacement, repair and retrofi t decisions along with associated superfl uous project costs. Timber frameworks are one of the most important and widespread types of timber structures. Their confi gurations and joints are usually complex and testify to a high-level of craftsmanship and a good understanding of the structural behaviour that has resulted from a long evolutionary process of trial and error. A simplifi ed analysis of old timber frameworks, considering hinged joints and only plane parts of the system, is often hard to realize. Old timber structures are usually highly statically indeterminate structures. This means that loads applied to the structure have different pathways to reach the supports. Resolving the indeterminate system involves looking for additional equations that actually express the relative stiffness of all those pathways. To illustrate how the differential stiffness of elements, joints or supports may infl uence the behaviour of the structure, a simple collar-braced roof is presented in Fig. 1. In the absence of buttressed walls, under vertical loads, the collar (or the tie-beam) is under tension because it prevents the roof from spreading. If buttressed walls restrain the feet of the rafters, the collar is in compression. The only difference between these situations is the horizontal stiffness of the supports (zero or infi nite). The mass of the walls to resist the outward thrust is not the only infl uencing factor. Most of the time, principal rafters are connected to wall plates that have to be stiff enough to act as a beam in the horizontal plane spanning between two fi xed ends in the walls. If the rafters are notched, for example, with birdsmouth joints, over the plate at the top, the roof can be hung from the ridge purlin, depending on the stiffness of the wall plate. The stiffness determines the ability of the wall plate to act as an additional support. This is valid for most types of carpentry joints as they usually are statically indeterminate. This simple example illustrates how the stiffness of joints may infl uence the force distribution inside the structure. This also points out that when restoring Thierry Descamps*, Coralie Avez**, Olivier Carpentier***, Emmanuel Antczak***, Gi Young Jeong****

Engineering and Patrimonial Buildings: Rewarding Interdisciplinary Work

The Our Lady Cathedral of Tournai in Belgium has been recognized in 2000 by UNESCO as a World Heritage site. However, today several parts of the Cathedral exhibit signs of weaknesses and interventions are needed. This article deals with the interdisciplinary approach followed for the study of the frameworks of the Cathedral. According to the historical study, the roof has exhibited different roofing materials throughout the ages. To make the contemporary architectural choices for the restoration, preliminary studies were initiated. Indeed, for the 800-year old frameworks of the transept, specific attention is needed to ensure that the substitution of the slate roofing by thick lead slates will not cause additional damages or pathologies. Through the study led by historians, archaeologists and engineers, this article gives a global overview of the preliminary studies performed by specialists in what could be considered as a good example of a rewarding interdisciplinary work. A special focus is made here on the work provided by engineers to understand all the specific problems of such a building and to propose respectful, efficient, and consistent solutions. The structural study of the Cathedral frameworks is mainly developed here coupled with on-site investigations and information led by historians and archaeologists to enlighten the structural behavior of the building.

Proposal of a CLT Reinforcement of Old Timber Floors

Despite the fact that, from the mechanical point of view, there is no ageing issues of timber elements when they are properly used, many old timber structures require important interventions because of changes in uses (which modifies the regulating rules for example), of material decay (misuse of timber) or possibly of a faulty design or construction. In particular, timber floors in old structures often present large deflections and most the time had been designed for a maximum load much lower than the one prescribed by contemporary rules. After an introduction about timber floors and a short review about the reinforcement technics that exist, the present paper presents a new proposal for their reinforcement. The solution developed in the present paper uses a Cross Laminated Timber (CLT) panel screwed over the existing floor, keeping a small gap between the panel and the existing joists. In this way, the new “composite” floor presents higher stiffness and the gap is used for horizontal line runs. For the design of such a “composite floor”, modified Johanssen’s equations (including the gap between the CLT panel and the joists) are proposed and their application on a case study is presented.

Repair and Strengthening of Traditional Timber Roof and Floor Structures

In many countries, traditional buildings comprise timber roof and floor structures. Most of these structures are degraded from different causes and need to be repaired or strengthened to ensure current and/or to fulfil the requirements of a new use of the building. Current knowledge assumes the need to preserve and to protect existing timber structural systems as a cultural value, with important advantages to the overall behaviour of the building. This growing sensibility towards the preservation and maintenance of heritage buildings has led researchers to study different repair and strengthening solutions. In the case of timber roof structures, this strengthening in many cases involves the connections between the roof structural members. Joint strengthening can be done with different methods, traditional or modern ones, using well-chosen materials, simple techniques or more sophisticated ones: from simple replacement or addition of new fasteners, to the use of timber or metal elements, glued composites, or even full injection with fluid adhesives. Each solution has advantages and disadvantages concerning conservation philosophy, architecture, aesthetics, construction issues and moreover unique consequences in engineering terms for the joint final strength, stiffness and ductility. All the above have to be evaluated in order the proper intervention to be chosen for each case. The main problem of existing timber floors is their low stiffness, which results in high bending deformations and vibrations under service loads. Permanent deflection due to creep can also reach critical values. Moreover, in earthquake prone areas, if seismic resistance has to be assured in existing masonry buildings, both roof and floor diaphragm behaviour must be achieved. This chapter aims to present a state-of-the-art review mainly on strengthening solutions for timber roof and floor structures, focusing on the most promising techniques taken into account the level of intrusion and reversibility. “Dry” interventions, based on timber or timber based elements will be highlighted.

Safety assessment of a high-rise dormitory in case of fire

Purpose This paper aims to focus on the combination of fire- and agent-based modelling approaches to assess the level of safety of a multi-storeyed building case study. Design/methodology/approach For an existing building to be occupied such as the engineering student dormitory of Mons (Belgium), engineers must establish, among the other things, that the building affords a sufficient level of safety during fire incident. This can be verified in accordance with prescriptive- and performance-based methodologies. The performance-based approach consists on using simulation tools such as fire dynamics simulator with evacuation to ensure/verify the level of safety required. In this paper, a model case study was built and then various scenarios have been implemented to answer some safety questions. Findings For this building layout, the results demonstrate that combining different egress components (i.e. stairs and outdoor ladders) has a negative impact on the evacuation process than using only the stairs to evacuate the building; phased evacuation strategy will not necessarily lead to faster evacuation; adding fire doors in the stairs and between the floors has a beneficial effect on the evacuation process. Originality/value This case study proposes some recommendations about adapted evacuation strategy and investments to improve the safety of high-rise student’s dormitory in case of fire.