Helena Johnsson

Defects in offsite construction: timber module prefabrication

The construction industry is based on craftsmanship. Quality control and assurance procedures applied in manufacturing cannot usually be readily applied in construction, where there are higher degrees of uniqueness in each project. One category of companies, industrialized housebuilders, is attempting to bridge some of the gaps between construction and manufacturing. These companies prefabricate building modules for later assembly at the building site. Since they are wholly responsible for large parts of the building process, these companies have greater opportunities to control and improve quality in a more consistent way than ordinary construction companies. Thus, it could be hypothesized that the frequency and severity of defects should be lower in industrialized housing than in ordinary construction. The aim of the study presented here is to examine this hypothesis by measuring and characterizing defects in industrialized housing. The design and manufacturing processes at two Swedish timber module prefabrication firms has been analysed through interviews, site visits and document reviews. Quality audits from three phases of the building process were compiled, analysed and categorized to provide statistical measures of defects in industrialized housing. The results show that the case study companies are better in terms of product quality than conventional housing.

Laboratory Tests and Numerical Analyses of Prefabricated Timber-Concrete Composite Floors

This paper describes tests on a novel composite floor system constructed by connecting prefabricated concrete slabs to timber joists. Seven types of shear connectors have been developed and tested: lag screws, either alone or combined with a notch cut from each timber joist; metal plates embedded in the concrete slab and either nailed or glued to the joists; dowels embedded in the concrete and glued to the timber; and toothed metal plates embedded in the concrete and pressed into the timber. Four-point bending tests to failure were performed on five, full-scale, 4.8 m long specimens connected with lag screws or metal plates nailed to the timber. Values of deflection and relative slip between the concrete slab and the timber obtained in these tests showed high correspondence with values obtained from a uniaxial finite element model developed for nonlinear analyses of composite beams. The model was also used to perform a numerical analysis to failure of composite beams with the other four connection systems that were developed but not tested on full-scale specimens. The outcomes of the experimental tests and numerical analyses show that the newly developed system can provide good structural performance, especially if connections with coach screws and notches in the timber are used. The economic advantages of prefabrication and the possibility to disassemble the structure and reuse the timber beams and concrete panels at the end of the service life make the proposed floor system very promising.

Platform use in systems building

The practice of reusing processes and technical solutions leads to the formation of product platforms in house building. Product platforms originate from industries employing a make-to-order production strategy, e.g. the automotive industry. To test how the product platform concept is useful in engineer-to-order production strategies, a case study at two Swedish house-builders was made. Key factors that affect platform use in systems buildings were sought. The smaller company operates a supplier-led platform focusing on commonalities in process knowledge. There is less definition of the product itself to allow for distinctiveness in the product offer. The larger company has a decentralized business and operates a client-driven platform with fragmented standardization. Focus is put on creating commonality through defining the product and handling distinctiveness through an iterative design procedure. Product families were not in use at the case study companies. The companies transform standardized platform solutions into project uniqueness by using support methods. Four platform support methods emerged from the case studies: design planning, collaborative design, design optimization, and requirements iteration. The balance between commonality and distinctiveness in the platform is important to attend to in each house-building project. The engineer-to-order production strategy hinders the implementation of a fully parameterized platform. The product platform concept is therefore expanded with support methods to handle distinctiveness, i.e. project uniqueness. The product platform assets: components, processes, relationships and knowledge, are present also in platforms used in systems building.

Construction Purchasing and Supply Chain Management

the subheadings are: sustainability optioneering in design; achieving sustainability value in construction procurement; valuing sustainability in properties; refurbishment and whole-life sustainability. This is a useful book for readers who want a quick update on changes which have happened in the quantity surveying profession in the UK in the last few decades. It covers a wide range of relevant issues. The author makes a real effort to, as stated in the preface, ‘... demonstrate beyond any doubt that the quantity surveyor is alive and well, adapting to the demands of construction clients, and ... looking forward to a long and productive future’ (p. xiv). This reviewer would suggest some improvements in future editions of the book, starting with the presentation. The formatting of the book makes its contents difficult to follow. For example, owing to similarities in the typeface of section headings, the hierarchy of the sections is not always clear. In Chapter 1, it is not clear whether ‘Measuring performance’ and ‘The British system compared’ are part of ‘The UK construction industry——a brief history’. Also, ‘Measuring performance’ appears twice (on p. 8 and p. 9) as headings of different sections. On p. 109, Table 4.6, point 4 in the right-hand column, it is not clear whether the figure which looks like a flower is intended to be part of the table. The annotations on it are not clear. In comparing the British and French systems of procurement and project management, the role of the quantity surveyor could have been considered. It would also have been useful if appropriate indications of the sources of the interesting and informative but rather brief history of the UK construction industry in Chapter 1 had been provided so that the interested reader could have found out more. The two chapters on sustainable construction could have been better coordinated to explain the concept and establish the opportunities which it offers the quantity surveyor to play a leading role in the construction industry. There are some gaps in the book. Topics which could have been discussed include how the quantity surveyor’s knowledge of LCC could be widened to life-cycle assessment, and given firmer theoretical grounding under the field of industrial ecology; and the role of the quantity surveyor in the carbon indexing of buildings. On ICT, the opportunities offered, and challenges posed, to the quantity surveyor by the current stress on building information modelling (BIM) could also have been discussed. The coverage of the international dimension in the book is inadequate. There is no discussion of such issues as: the differences in the practice of quantity surveying in different countries where the profession has spread; the efforts by the RICS to establish a global reach (culminating recently in the election of its first non-UK president). The recent widening of the spread of the profession into various countries through the establishment of surveying practices or introduction of new educational programmes, as well as the consolidation of quantity surveying firms in international partnerships, and the formation of global multi-disciplinary consultancy firms could also have been discussed. Another useful subject would have been what the quantity surveyor can learn from the way in which the cost consultancy function is undertaken in other countries. This reviewer suggests that in subsequent editions, the author should really establish the claim in the preface that ‘the quantity surveyor continues to prosper, with interest in the profession never higher’ (p. xviii).

Production strategies for pre-engineering in house-building: exploring product development platforms

Construction is a trade where the dominating production strategy is engineer-to-order. House-builders can pre-engineer their design to different degrees, resulting in variations of the engineer-to-order strategy: design-to-order, adapt-to-order, and engineer-to-stock. This variation causes different settings for the use of platforms in house-building. The aim of this research is to diversify the engineer-to-order production strategy and its consequences for platform organization by studying its use in house-building. The multiple case study on four engineering/contractor firms reports the core capabilities for engineer-to-order firms: procurement and tendering, market knowledge, engineering, multi-skilled manufacturing, and coordination of sales and manufacturing. Design-to-order, adapt-to-order and engineer-to stock were shown to be production strategies in use in house-building. In design-to-order platforms parts of the platform are undefined while engineer-to-stock platforms are fully predefined. Coordination between market and manufacturing is a crucial capability when engaging in platform organization. When an engineering firm and a contractor collaborate to fulfil client needs, the coordination capability between market and manufacturing was shown to be low. The case study shows that specialized contractors who integrate the supply chain towards a specific market segment benefit fully from the platform concept, while contractors with a wider scope could focus on standardization of processes rather than products.

Provisions for Ductile Behavior of Timber-to-Steel Connections with Multiple Glued-In Rods

AbstractConnections with glued-in rods are very efficient, high-strength joints and can be successfully used, for example, for the anchorage of vertical timber elements to a foundation. Although extensive research was done on the pullout strength of single rods, few references can be found on the behavior of multiple glued-in rods. This paper presents the results of an experimental program carried out on timber-to-steel connections with multiple glued-in rods. Two series of 10 specimens with four large-diameter, glued-in rods made from mild steel (Series GB) and 10 specimens with 12 small-diameter, high-grade glued-in rods (Series GS) were tested to failure under monotonic tensile load. Both types of connections ultimately failed in a brittle manner; however, the GB series developed some plastic deformations prior to failure which was caused by the pullout of two rods and longitudinal splitting of the timber member. By comparing the experimental results with the analytical predictions, no significant grou...

A study of a plan-do-check-act method used in less industrialized activities : two cases from industrialized housebuilding

In construction projects, a large number of deviations are usually found during inspections and adjusted in a reactive manner. For projects to become proactive, root causes need to be identified and eliminated as a part of a process of continuous improvement (CI). Plan-do-check-act (PDCA) methods are part of CI and have been used with success within the manufacturing industry for decades. Research studies of PDCA in construction are less common, which could be explained by the past dominance of the project-based nature of construction compared to the process-based nature of manufacture. Industrialized construction, however, has changed this picture somewhat, and it is of interest to find out how well it works for less industrialized activities in construction. A PDCA method was tested in two cases selected from one medium-sized Swedish industrialized housebuilder, which uses a building system based on offsite manufactured modules. Empirical results are based on systematic data gathered through interviews and participant observations. Results from the two cases show that the PDCA method worked even when processes were divided into industrialized parts within a factory and non-industrial parts at the construction site although this might lead to temporary corrective actions rather than permanent process actions.

Plug shear failure in nailed timber connections: Load distribution and failure initiation

Brittle failures in mechanical timber joints should be avoided, because this often results in low capacity and brittle failure of the structure. Nailed joints experience three ultimate failure modes: embedding, splitting or plug stear failure. To avoid plug shear failure, short and wide joints are preferred, limiting the number of fasteners in line with the load and grain direction. Plug shear failure was examined in short-term experiments on nailed steel-to-timber joints in glulam loaded in tension parallel to the grain with five different joint geometries. The aim of the study was to examine if the fastener group layout can be adjusted to avoid plug shear failure and to gain an insight into the causes of failure initiation. Using spring models, it is shown that the load distribution creates pronounced stresses at the last nail in the joint, which probably initiates the plug shear failure. Test results are compared with prediction models found in the literature. It was found that fasteners placed in groups can be a successful way of reducing the risk of plug shear failure. The failure is probably initiated at the nail farthest from the free end, where tensile stresses perpendicular to grain occur.ZusammenfassungSprödbruch in mechanischen Holzverbindungen sollte vermieden werden, da dies vielfach zu einer geringen Tragfähigkeit und Sprödbruch in der gesamten Konstruktion führen kann. In genagelten Holzverbindungen können insgesamt drei Brucharten auftreten: Bruch durch Überschreitung der Lochleibungsfestigkeit, Aufreissen, oder Ausreissen des gesamten genagelten Bereichs. Um solche Scherbrüche zu vermeiden, sind kurze und breite Verbindungen zu bevorzugen, bei denen die Anzahl der Verbindungsmittel in Last- und Faserrichtung begrenzt wird. Das Schubversagen wurde in Kurzzeitversuchen an Holz-Stahl-Nagelverbindungen von Brettschichtholz bei Zugbeanspruchung parallel zum Faserverlauf mit fünf verschiedenen Verbindungsgeometrien geprüft. Ziel der Untersuchung war, festzustellen, ob die Nagelanordnung so gewählt werden kann, dass Schubversagen vermieden wird, und um Einblicke in die Ursache von Bruchauslösung zu gewinnen. Mit einem Federmodell kann gezeigt werden, dass die Lastverteilung erhebliche Spannungen am letzten Nagel in der Verbindung verursacht, wodurch aller Wahrscheinlichkeit nach das Schubversagen entsteht. Versuchsergebnisse wurden mit theoretischen Modellen aus der Literatur verglichen. Es stellte sich heraus, dass gruppenweise angeordnete Verbindungsmittel das Risiko eines Schubversagens deutlich vermindern können. Wahrscheinlich beginnt der Bruch an dem vom freien Ende am weitesten entfernten Nagel, wo Zugspannungen quer zur Faser auftreten.

Prefabricated timber walls anchored with glued-in rod connections: racking tests and preliminary design

A new beam and post system for multi-storey timber buildings has been developed in Sweden. The building is braced with timber walls constructed from two Kerto-Q LVL boards glued and screwed onto a glulam frame. The walls are prefabricated off-site and can be connected to the foundation using either glued-in steel rods with metric thread or nail plates. Introductory racking tests of full scale walls anchored with glued-in threaded rods were performed. The paper presents the results of the experiments and discusses the use of the transformed section method to predict racking capacity of the anchored wall. To evaluate the strength of the glued-in rods, a newly proposed model was employed. An analytical study was conducted to investigate the role of the sheathing and the contribution of the axial force on the racking capacity of the walls. The wall panels tested in this experimental programme showed high strength and stiffness under racking load. The anchoring joints with glued-in steel rods with metric thread demonstrated a high load-carrying capacity with, however, large scatter and a brittle failure mode characterized by pull-out from the timber member. The transformed section method was successfully used to predict the racking capacity of timber walls anchored with glued-in steel rods.ZusammenfassungIn Schweden wurde ein neues Ständerbausystem für mehrgeschossige Holzgebäude entwickelt. Das Gebäude ist mit Wandelementen ausgesteift, die aus einem Rahmen aus Brettschichtholz und zwei darauf verklebten und verschraubten Kerto-Q Furnierschichtholzplatten bestehen. Die vorgefertigten Wände können entweder mittels eingeklebter Gewindestangen mit metrischem Gewinde oder mit Nagelplatten auf dem Boden verankert werden. An originalgroßen Wänden, verankert mit eingeklebten Gewindestangen, wurden Wandscheibenversuche durchgeführt. In dieser Studie werden die Versuchsergebnisse vorgestellt und ein Modell zur Bestimmung der Tragfähigkeit von verankerten Wandscheiben diskutiert. Die Festigkeit der eingeklebten Gewindestangen wurde mit einem neu entwickelten Modell bestimmt. Der Beitrag der Beplankung und der axialen Kraft zur Wandscheibentragfähigkeit wurde in einer analytischen Studie untersucht. Die untersuchten Wandtafeln wiesen bei einer Wandscheibenbelastung eine hohe Festigkeit und Steifigkeit auf. Die Verankerung mit eingeklebten Stahlstangen mit metrischem Gewinde wies eine hohe Tragfähigkeit auf, jedoch mit großer Streuung und einem spröden Bruchverhalten, das durch Herausziehen der Gewindestangen aus dem Holz gekennzeichnet ist. Das entwickelte Modell erwies sich als erfolgreich zur Bestimmung der Wandscheibentragfähigkeit von Wandelementen, die mit eingeklebten Stahlgewindestangen verankert sind.

3D Computer Visualization in Timber Construction—Some Important Parameters

Abstract Timber building structures are seldom considered because of a lack of timber construction knowledge among many clients and professionals. 3D computer visualization (3D VIZ) is a possible way of communicating the aesthetics of a visible timber structure and visualizing complex timber connections. This paper investigates the potential for 3D VIZ to communicate visible timber structures during the different phases of the construction process. Furthermore, important parameters (controllable in 3D VIZ) for communicating a timber structure are identified. Through an Internet-based Delphi study, the usefulness of 3D VIZ for timber structures has been evaluated by professionals representing different competencies in the construction process. The results show that structural complexity, intended beholder (professional or non-professional) and current construction phase influence the benefit of 3D VIZ. The level of detail in the visualization is heavily dependent on whether the communication is internal (between professionals) or external (between professionals and clients/users). The impact of parameters needed, such as textures, surface structures and realistic lighting, have been described.