Full-size Walls Research Articles

Nonlinear FE-analysis and testing of light-frame timber shear walls subjected to cyclic loading

Light-frame timber shear walls have been used as load-bearing elements in buildings for several decades. To predict the performance of such structural elements under loading, numerous analytical and numerical models have been developed. However, little focus has been on the prediction of the plastic damage behaviour and unloading of the walls. In this paper, a parametric Finite Element (FE) model is further developed by introducing elasto-plastic connectors to simulate the mechanical behaviour of the sheathing-to-framing connections. To verify the accuracy of the elasto-plastic model, full-size walls were tested and compared with results from simulations. The numerical results, from a few loading cycles, indicate that the model achieves reasonable accuracy in predicting both the nonlinear elastic and plastic deformations. Both experimental and simulation results demonstrate the importance of opening locations relating to the external racking force. The results also indicate that for a double-layer wall, its racking strength can be achieved by summation of the separate contribution from each layer. Furthermore, the internal layer was observed to contribute significantly less than the external layer since its nail pattern was based on the sheathing pattern of the external layer.

Experimental Investigation of Concrete Sandwich Walls with Glass-Fiber-Composite Connectors Exposed to Fire and Mechanical Loading

Precast concrete sandwich panels (PCSPs) are known for their good thermal, acoustic and structural properties. Severe environmental demands can be met by PCSPs due to their use of highly thermally insulating materials and non-metallic connectors. One of the main issues limiting the wider use of sandwich walls in construction is their unknown fire resistance. Furthermore, the actual behaviour of connectors and insulation in fire in terms of their mechanical performance and their impact on fire spread and the fire resistance of walls is not fully understood. This paper presents an experimental investigation on the structural and thermal behaviour of PCSPs with mineral-wool insulation and glass-fiber-reinforced polymeric bar connectors coupling two concrete wythes. Three full-size walls were tested following the REI certification test procedure for fire walls under fire and vertical eccentric and post-fire mechanical impact load. The three test configurations were adopted for the assessment of the connectors’ fire behaviour and its impact on the general fire resistance of the walls. All the specimens met the REI 120-M criteria. The connectors did not contribute to the fire’s spread and the integrity of the walls was maintained throughout the testing time. This was also confirmed in the most unfavourable test configuration, in which some of the connectors in the inner area of the wall were significantly damaged, and yet the structural connection of the concrete wythes was maintained. The walls experienced heavy heat-induced thermal bowing. The significant contribution of connectors to the stiffness of the wall during fire was observed and discussed.

Three-dimensional stress analysis and design of cross-laminated timber panels using full-layerwise-theory-based finite element method

Cross-laminated timber (CLT) panels have an increasing market share and extensive application in civil engineering, as full size walls or light floor structures. Due to their low environmental impact, excellent thermal characteristics and high mechanical performance, they are being extensively applied instead of conventional mineral-based building materials. Thick and orthogonal structure of CLT provides the considerable stiffness with the low weight and makes such panels particularly suitable in seismic-prone areas. The ease of assembly allows prefabrication and reduces construction time and cost.Current models for calculating the stress-deformation state of a CLT loaded out-of-plane mainly emerged from the long tradition of using very simple one-dimensional (beam-like) elements in timber structures. The paper tends to overcome some limitations of the current models by using the full-layerwise plate theory (FLWT) of Reddy, serving as a basis for the implementation of layered finite elements. The proposed model accounts for the complex 3D stress state in CLT loaded out-of-plane and implies an original procedure for stress calculation. It is implemented using the original object-oriented MATLAB framework, while the graphical user interface for pre- and post-processing is developed using GiD.The presented approach is validated using the available numerical and experimental data in the literature, and compared against the commonly used methods for the design of CLT. Finally, the 3D stress-deformation state in the CLT slab of complex shape (commonly used in building structures) is obtained using the FLWT-based finite elements. The results are validated against the numerical data from the commercial software, and then used for checking of the ultimate and serviceability limit states for CLT slab according to Eurocode 5. Excellent agreement of the obtained results confirmed the potential of the proposed model to become a promising tool for engineering design of CLT slabs of arbitrary geometry.

Experimental investigations of sandwich panels using high performance concrete thin plates exposed to fire

Structural sandwich panels using thin high performance concrete (HPC) plates offer a possibility to address the modern environmental challenges faced by the construction industry. Fire resistance is a major necessity in structures using HPC. This paper presents experimental studies at elevated temperatures for panels with 30 mm thick plates stiffened by structural ribs, thick insulation layers, and steel shear connecting systems. Parametric variation assessing the role of each component of the sandwich structure was performed on unloaded specimens of reduced size. Full size walls were tested with load. Tests were performed in standard furnaces, following the conditions of REI certification tests. Unloaded specimens successfully passed tests. Loaded specimens met the R and I requirements, failing E due to sustained flaming of the insulation. They exhibited multiple cracking of their exposed plate and one of them experienced heavy heat-induced spalling. Results highlighted insulation shear failure from differential thermal expansion at the interface with concrete. It suggests the existence of a high bond level between the two materials which might allow structural applications at early age. Cracks resulted from buckling and thermal bowing, present in the upper and lower parts of the panel. Shear connectors created stress concentrations leading to local failure. Only ribs were found to have a structural role, the plate being largely negligible and solely protecting the insulation from heat. Performance could be enhanced by using thicker plates (50 mm).

G17 Transforming the design of a children’s emergency department – simulation as a powerful service development tool

AimTo utilise large scale simulation to assess the full system functioning of a children’s emergency department prior to actually constructing the building. The simulation aimed to identify the impact of...

Rehabilitation of Masonry Walls Using Unobtrusive FRP Techniques for Enhanced Out-of-Plane Seismic Resistance

Earthquake damage to unreinforced masonry buildings has shown the vulnerability of perimeter walls to out-of-plane failure. This paper describes a study that was carried out to develop and test innovative fiber reinforced polymer (FRP) rehabilitation techniques that meet the stringent requirements for strengthening historical buildings and to be cost-effective alternatives applicable to other existing masonry structures. Unobtrusive FRP rehabilitation techniques that utilize flexible carbon fiber composite cables, mounted near the surface of the facade walls in epoxy-filled grooves in the bed and head joints, were developed. Ten full size walls were constructed of clay bricks and retrofitted using the developed FRP rehabilitation techniques. The test results demonstrated the high efficiency of the rehabilitation techniques under both monotonic and quasistatic cyclic loadings. Significant increases in ultimate capacities, energy absorption, and deformability were achieved for various reinforcing schemes co...

A New Look at the Control of Volume Change Cracking of Base Restrained Concrete Walls

Volume change cracking is a widespread problem in base restrained concrete walls. In such walls the degree of restraint is not uniform, but depends on the wall length/height ratio and on the position of the point in consideration within the wall itself. A two dimensional finite element analysis was carried out on walls with different L/H ratios to determine the variation of restraint within these walls. Also crack width was proved to be directly related to the change of restraint in the wall before and after cracking. From the restraint factors obtained, idealized diagrams of the change of restraint were prepared. These diagrams were used to determine the exact amount of steel reinforcement that is required for the control of volume change cracking in the walls. Steel reinforcement was provided in positions where it is really effective in controlling these cracks. Therefore, variable steel quantities were used in the walls. This led to the effective reinforcement concept. This concept and the proposed method for the control of cracking in walls were tested against the cracking data obtained from 37 full size walls and 8 experimental walls. The comparison showed good agreement between the theoretical and observed width of cracks.

A study of the behaviour of volume change cracking in base restrained concrete walls

The present work studies the problem of cracking due to volume change of base restrained reinforced concrete walls. The cracking behaviour of some 61 full size walls and 14 experimental walls was investigated. The observed primary and secondary crack spacings and widths were compared with the values obtained using recently developed formulas and with formulas developed previously. Good agreement was found between the observed values and those predicted using the developed formulas.

The flexural strength of concrete blockwork

Synopsis The results of a large number of flexural strength tests on wallettes (small masonry panels for testing) made with a range of commercially available concrete blocks are reported. The relationships between the performance of the wallettes and several properties of the block were investigated as a possible basis for a table of characteristic flexural strength values in BS 5628: Part 1: 1978, ‘the Code of Practice for Structural use of masonry’. In general, the basis chosen, compressive strength, and the levels set in the Code are satisfactory but the margins of safety may be lower for masonry made with some types of blocks and for thicker walls. Interim results for full-size walls are also given which confirm the trends indicated by the tests on wallettes.

Finite Element Analysis of Wood-Stud Walls

A theoretical procedure based on the finite element model and linear step-by-step analysis for evaluating the behavior of wood-stud walls under combined bending and compression loads was developed and verified. The procedure accounts for the variations in material properties, nonlinear material behavior of studs, partial composite action and slip among the components, and the load sharing among the studs of various strengths and stiffnesses. I-beam wall sections and full-size walls are tested to verify the procedure. Theoretical and experimental deflections and slips at service loads and overloads, and the ultimate load of the tested wall panels showed good agreement. Parameter study investigating the effect of the joint and wall covering stiffness on the ultimate load is included. The developed procedure can be used to obtain the information necessary for improved structural and economic design of wood-stud walls for residential and commercial buildings.