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.
Cross-laminated timber (CLT) panels have proved their efficiency as vertical and horizontal load-carrying structures, and their design methods for serviceability and ultimate limit states are well defined. However, there is a lack of more general and versatile analytical methods for the ultimate load carrying capacity determination of CLT structures. In this paper, the classical layered beam theory is adopted for the ultimate failure load estimation of axially compressed CLT panels. The proposed method retains its accuracy both with an asymmetric layer setup and when the number of CLT layers exceeds five. The presented method is validated by adopting experimental test data from two test series produced by other researchers.
This paper analyses the analytical formulations for the lateral elastic deformation of Light Timber Framed (LTF) and Cross-Laminated Timber (CLT) shear walls according to the new Eurocode 5 (EC5) proposal. Finite Element (FE) models and the Standard predictions are compared by emphasizing the role of each deformation contribution. A total of 1830 comparisons between analytical and numerical estimations are carried out by exploiting the Application Programming Interface of SAP2000 to modify the FE model parameters automatically. The parametric analyses proved that the numerical and analytical predictions are pretty consistent. Furthermore, in both LTF and CLT shear walls, the estimates for in-plane shear and rigid body sliding are in excellent agreement. Conversely, the analytical formulas for kinematic rocking are generally conservative for LTF and monolithic CLT shear walls, with an approximate 18%–19% discrepancy. The analytical expressions of the upcoming EC5 perfectly match the numerical model for segmented CLT shear walls under lateral forces and no vertical load. However, the presence of the vertical load determines a significant bias. Additionally, the predictions for bending deformations are not in good agreement. Therefore, the paper discusses possible enhancements for the equations proposed in the next generation of Eurocodes for the rocking deformation of segmented CLT walls to better conform with FE predictions.
Effects of fastener type, end distance, layer arrangement, and panel strength direction on lateral resistance of single shear lap joints in cross-laminated timber (CLT)
This research investigated the effects of the fastener type, end distance, layer arrangement, and panel strength direction on the lateral resistance of nailed and screwed single shear lap joints in CLT panels. Three-ply CLT panels were made out of poplar wood (Populus alba) with two layer arrangements: 0/90/0 ° and 0/45/0 °. The lateral resistance of nine types of fasteners with end distances of one, two, and three centimeters in two major and minor strength directions of CLT panels was measured by Instron (model 4486) testing machine. The major axis of CLT panels with the 0/45/0° arrangement showed the highest lateral resistance; however, its minor axis showed the lowest one. Among fasteners, Lag screws (10 mm) had the highest lateral resistance, while steel nails had the weakest. In all CLT samples, by changing the fastener type, end distance, layer arrangement, and panel strength direction, the lateral resistance changed 155.8 %, 72.1 %, 3.3 %, and 19.6 %, respectively. Furthermore, changing the failure mode of the fasteners from Im to IV, and CLT members from shear to bearing mode due to the increase in the end distance enhanced lateral resistance, leading to ductile behavior. The NDS, Eurocode 5, and CSA 086 theoretical models were applied to predict the yield lateral loads of the connections. The results showed that Eurocode 5, and CSA 086 better predicted the lateral load of connections with MAPE of 33.8 % and 34.24 %.
This paper investigates the effect of screw reinforcement on the capacity of timber members under compression perpendicular to the grain. The predictions of existing capacity models are compared to the experimental results of 39 timber specimens, distinguished by different load, screw and geometric configurations. Current capacity models assume two failure mechanisms, mainly characterized by their location, i.e. the contact area of the applied load (first mode) or the screw tips (second mode). However, the experimental tests reveal that the second mode never occurs despite the model predicting the occurrence of the second mode in more than half of the tested specimens. Additionally, the experimental tests show the fallacy of existing models in accurately estimating the capacity associated with the second failure mode. Parallely, the model appears to be relatively conservative for the first failure mode.
Timber-concrete composite systems are a high-performance alternative for building floors, of great interest in the current context of environmental concerns. Looking for a more eco-friendly solution, the paper presents a new flooring system with a wood-concrete connection that does not require adhesives or special metal elements. Four-point bending tests were performed on TCC flooring samples with a span of 6.0, 7.2 and 8.4 m. Its cross section was a prefabricated piece in the shape of an inverted T made up of a lower glulam flange, glued together with a central plywood rib with aligned holes in its upper part that go through the entire thickness of the plywood. The set was completed with a top layer of poured-in-place concrete. The connection between both materials is achieved by penetrating the concrete into the rib holes. Additionally, corrugated steel bars were placed through said holes to achieve ductile behaviour. In all cases, a slenderness ratio of L/24 was used. The experimental results showed that the lowest value of ultimate load obtained was 4.3 times higher than the total service load estimated for a building for public use (9 kN/m2). The maximum deflection of the total load was between L/573 and L/709 for the loads corresponding to a building for public use (9 kN/m2) and between L/1069 and L/1340 for the case of residential type building (5 kN/m2). An analysis of the effects of vibrations in the service limit state in relation to user comfort has been included. The results indicate that the system satisfies the requirements for the intended uses.
Consequently, the proposed solution shows its effectiveness both in terms of strength and stiffness for the construction of light floors, being easy to build and having high performance.
As a building material, engineered bamboo has caught attention around the world due to its advantages in energy conservation and environmental protection. The seismic performance of bamboo buildings needs to be evaluated to further promote the use of bamboo materials in building construction. We studied the seismic response of a 3-story bamboo frame structure numerically using nonlinear dynamic time history analysis. A simplified modeling method for bamboo column-beam joints was proposed in the numerical model. The hysteresis behaviour of the joint was simulated by Pinching 4 material in OpenSEES, with the parameters calibrated through test results. Comparative analysis shows that the proposed modeling method could reasonably reflect the pinching effect and the degradation of the joint hysteretic behavior. A total of 20 ground motions with three intensities were involved in the nonlinear dynamic analysis. The results demonstrate that the frame meets target performance levels, providing evidence for the further popularization of engineered bamboo structures.
Walls, as components of the lateral-force-resisting system of a building, are defined as shear walls. This study aims to determine the behavior of shear wall panel cross-laminated-timber-based mangium wood (Acacia mangium Willd) (CLT-mangium) in earthquake-resistant prefabricated houses. The earthquake performance of CLT mangium frame shear walls panels has been studied using monotonic tests. The shear walls were constructed using CLT-mangium measuring 2400 mm × 1200 mm × 68 mm with various design patterns (straight sheathing, diagonal sheathing/45°, windowed shear wall with diagonal pattern and a door shear wall with a diagonal pattern). Shear wall testing was carried out using a racking test, and seismic force calculations were obtained using static equivalent earthquake analysis. CLT-mangium sheathing installed horizontally (straight sheathing) is relatively weak compared to the diagonal sheathing, but it is easier and more flexible to manufacture. The diagonal sheathing type is stronger and stiffer because it has triangulation properties, such as truss properties, but is more complicated to manufacture (less flexible). The type A design is suitable for low-intensity zones (2), and types B, D, E1 and E2 are suitable for moderate-intensity zones (3, 4), and type C is suitable for severe-intensity zones (5).
Reducing the embodied and operational energy of buildings is a key priority for construction and real estate sectors. It is essential to prioritize materials and construction technologies with low carbon footprints for the design of new buildings. Off-site constructions systems are claimed to have the potential to deliver a low carbon build environment, but at present there are a lack of data about their real environmental impacts. This paper sheds lights on the environmental performance of two offsite technologies: cold formed steel and cross laminated timber. Specifically, the environmental impacts of a CFS technology are discussed according to six standard impact categories, which includes the global warming potential and the total use of primary energy. The study is based on a detailed cradle to gate life cycle analysis of a real case study, and discusses the impacts of both structural and non-structural components of CFS constructions. As a useful frame of reference, this work compares the environmental impacts of 1 m2 of walls and floors of CFS technology with those of cross laminated timber, which is spreading as innovative off-site technology for the development of nearly zero energy buildings, and a conventional reinforced masonry technology, which is largely adopted in the Italian construction sector. The paper concludes with the necessity to optimize structural systems to reduce the overall embodied carbon impacts.
Wood use is expanding to new markets, driven by the need to substitute fossil-intensive products and energy. Wood products can contribute to climate change mitigation, if they have a lower fossil footprint than alternative products serving the same function. However, the climate change mitigation potential is contingent on the net fossil and biogenic emissions over time, as well as the realism of the counterfactual scenario and market assumptions. This study aims to improve the consistency of assessing the avoided fossil emissions attributed to changes in wood use, and to estimate the additional mitigation potential of increased wood use in construction and textile markets based on wood harvested in Finland. The results show that, compared to baseline, an increase in the market share of wood leads to an increase in atmospheric CO2 concentration by 2050. Thus, the substitution impacts of wood use are not large enough to compensate for the reduction in forest carbon sinks in the short and medium term. This outcome is further aggravated, considering the decarbonization of the energy sector driven by the Paris Agreement, which lowers the fossil emissions of competing sectors more than those of the forest sector. The expected decarbonization is a highly desirable trend, but it will further lengthen the carbon parity period associated with an increase in wood harvest. This creates a strong motive to pursue shifts in wood uses instead of merely expanding all wood uses.
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