Boundary layer effect in composite beams with interlayer slip

International audienceAn apparent analytical peculiarity or paradox in the bending behavior of elastic-composite beams with interlayer slip, sandwich beams, or other similar problems subjected to boundary moments exists. For a fully composite beam subjected to such end moments, the partial composite model will render a nonvanishing uniform value for the normal force in the individual subelement. This is from a formal mathematical point of view in apparent contradiction with the boundary conditions, in which the normal force in the individual subelement usually is assumed to vanish at the extremity of the beam. This mathematical paradox can be explained with the concept of boundary layer. The bending of the partially composite beam expressed in dimensionless form depends only on one structural parameter related to the stiffness of the connection between the two subelements. An asymptotic method is used to characterize the normal force and the bending moment in the individual subelement to this dimensionless connection parameter. The outer expansion that is valid away from the boundary and the inner expansion valid within the layer adjacent to the boundary (beam extremity) are analytically given. The inner and outer expansions are matched by using Prandtl’s matching condition over a region located at the edge of the boundary layer. The thickness of the boundary layer is the inverse of the dimensionless connection parameter. Finite-element results confirm the analytical results and the sensitivity of the bending solution to the mesh density, especially in the edge zone with stress gradient. Finally, composite beams with interlayer slip can be treated in the same manner as nonlocal elastic beams. The fundamental differential equation appearing in the constitutive law associated with the partial-composite action in a nonlocal elasticity framework is discussed. Such an integral formulation of the constitutive equation encompassing the behavior of the whole of the beam allows the investigation of the mechanical problem with the boundary-element method

Horizontal Stabilisation of Sheathed Timber Frame Structures Using Plastic Design Methods – Introducing a Handbook Part 3: Basics of the Plastic Design Method

AbstractDesign of shear walls has been a topic of major discussions to develop a common European code for design of timber structures. The main problem has been that shear walls are fastened to the substrate in different ways in different countries and that this fact must be reflected in the code. In this part the requirements are given that must be met for the ductile characteristics of the sheathing-to-framing joints in order for the plastic design method to be applicable. The method is based on the plastic lower bound theory. The fundamental prerequisites for the method are that the static equilibrium for the structure is fulfilled and that the sheathing-to-framing joints are ductile. What requirements that should be made on the mechanical properties of the joints for the plastic design methods to be applicable and the precaution measures to take to avoid brittle behaviour are discussed. The two main principles for anchoring of sheathed timber frame shear walls, fully and partially anchored, are illustrated showing the static behaviour of the walls and the force distribution in the framing members and the sheathings. In addition, a general description of the design in the serviceability limit state is given. For medium-rise and taller buildings the serviceability limit state needs to be taken into account. There are no specified criteria for deformations in the present code

Wood in Buildings : Technical and business development of wooden buildings, especially multi-storey timber buildings

Wood plays an important role in the construction industry to meet the challenges of the climate, finite natural resources and energy consumption. It plays a significant role in environmental and climate effects on society as well as the well-being of its individual citizens. Multi-storey wooden buildings in the Nordic region have proven to be the main business opportunity in the new bioeconomy. However, it is emphasized that the technical challenges must first be overcome and access on design tools come to the same level as the equivalent for concrete and steel. The future potential for increased construction of multi-storey wooden buildings has also recently been studied. It emphasizes that based on demographics (strong population growth and strong urbanization), climate (climate impact reduction) and employment (keeping employment at a high level with a “reasonable” distribution of jobs between urban and rural areas), industrial timber construction can contribute as follows until 2025: (1) Build capacity for industrial timber construction to be able to deliver 50 % of the multi-storey houses in wood on the Swedish market; (2) Create 8 000 new jobs in prefabrication companies and help relocate 6 000 jobs from big cities to the countryside. Business development focuses on identifying opportunities and developing resources for new, expanded or changed business operations. For the construction industry, this means to create business models for the building process, including design, manufacturing and construction, and involve consultants, contractors and small and large suppliers. Business models are linked to current technical activities. When business models and technologies interact, this connection needs to be a starting point. We need to link industrial construction with companies’ business models. Business models for industrialized construction of multi-storey wooden houses that are in focus can provide a better understanding of its potential for competitiveness and profitability. Industrialized construction is also a driving force in shaping new or changing business models. The work comprises of three main activity areas: (1) the technical part, (2) the business part, and (3) the application part. Technical part: This part includes developing different types of design tools that the industry needs to produce and build multi-storey buildings in wood. Mainly within the areas (1) architecture and building design; (2) structural engineering – building systems, horizontal stabilization and sway, robustness, components and connections. Business part: This part includes developing business models for wood building projects, especially for multi-storey wooden buildings. Especially for the industrialized manufacturing and construction processes, integration of SME’s into big wood construction projects, and interaction between the different market players. Developing business models for industrialized multi-storey wooden buildings would include adapting a general business model to the industrialized building setting and choose the major business model elements, identify frequently used business models and model elements, and establish a good fit between the business model its model elements. The business model elements include prefabrication mode, role in the building process, end-user segments, offering, and resources for design and onsite construction. Application part – demo and pilot projects: This part includes following up on real wood building objects under and after construction, to identify weaknesses and challenges for learning and further study. And studying the industrialization of the wood construction process from manufacturing to erecting and the digitization with respect to planning and design. Critical issues to evaluate are:(1) Horizontal stability, robustness and building sway;(2) Business models and business elements; planning, management and interaction between participating partners (consultants, wood companies, entrepreneurs) and between main supplier (“locomotives”) and subcontractors (SME’s); and(3)     Industrialisation and digitization of the different processes.Funder: Skellefteå and Piteå municipalities; Swedish Federation of Wood and Furniture Industry (TMF); Soksbo; Derome; Folkhem</p

Dynamic fail-safe behaviour of steel structures

The fundamental behaviour and the capacity of steel structures subjected to loss of interior load-bearing elements are studied. The ultimate load-bearing and deformation capacity of certain beam-to-column connections and the dynamic fail-safe behaviour of some ordinary steel structures are investigated in detail. A number of different geometrical models of steel structures in the area of primary damage are analysed. Both bending and catenary action of the models are treated and the strength properties of both members and connections are considered. Two types of connections are investigated, viz. the "bolted heel connection" and the bolted end-plate connection (with a degree of moment rigidity of 25%). No stability problems are treated. A rigid-body method of analysis is applied. Design methods for the bolted heel and bolted end-plate connections under catenary action are proposed, which safely predict the over-all behaviour and the ultimate load-bearing and deformation capacity of each connection. For structures having these two types of connections, the static damage endurance capacity under catenary action is approximately equal. The applicability and accuracy of the riqid-body method is evaluated. The accuracy is determined by comparison with an elasto-plastic vibration theory and an equivalent mass-spring method. The rigid-body model proves to be a suitable model in order to determine the failsafe behaviour of most steel structures. The ultimate dynamic load-bearing capacity under bending action regarding member characteristics and under catenary action regarding partly member characteristics and partly joint characteristics is evaluated in great detail. It is found that the dynamic capacity under bending action approximately equals the static one provided that the greater deformations obtained under dynamic conditions can be absorbed. No regard to the time of removal of the load-bearing element is thus necessary if only the deformation capacity of the structure is verified. Also, strain-hardening effects and geometrical non-linearity need not be considered. The dynamic capacity under catenary action regarding member characteristics is only half of the static one, and regarding joint characteristics only one third of the static one for structures with bolted heel connections, and half of the static one for structures with bolted end-plate connections. The high efficiency of catenary action compared to bending action found under static conditions, is reduced considerably under dynamic conditions. For many practical cases only full end constraints, momentary loss of load-bearing elements and geometrical linearity need to be considered. The maximum column reactions at ultimate dynamic load always fall below the maximum reactions at ultimate static load. Deflections and reactions determined theoretically from the rigid-body models employed agree well with those measured.Godkänd; 1980; 20070503 (ysko

Provning av tvärböjning och spjälkning av syllen i partiellt förankrade skiv-regelväggar

Godkänd; 2014; 20141219 (ulfgir

Tests and Analyses of Slotted-In Steel-Plate Connections in Composite Timber Shear Wall Panels

The authors present an experimental and analytical study of slotted-in connections for joining walls in the Masonite flexible building (MFB) system. These connections are used for splicing wall elements and for tying down uplifting forces and resisting horizontal shear forces in stabilizing walls. The connection plates are inserted in a perimeter slot in the PlyBoard™ panel (a composite laminated wood panel) and fixed mechanically with screw fasteners. The load-bearing capacity of the slotted-in connection is determined experimentally and derived analytically for different failure modes. The test results show ductile postpeak load-slip characteristics, indicating that a plastic design method can be applied to calculate the horizontal load-bearing capacity of this type of shear walls