The design and construction of temporary military structures has changed little since World War II. While these structures are lightweight and rapidly deployable, they require a sizeable workforce to construct and provide minimal ballistic and blast protection for occupants. Cross-laminated timber (CLT) is a relatively new prefabricated engineered wood product that is strong, stiff, quick to build, and has the potential to offer inherent ballistic and blast resistance compared to traditional wood products. The orthotropic nature of CLT coupled with the energy absorbing capacity of the thick wood panels warrant further investigation into the viability of CLT for temporary military structures. To that end, the research presented in this thesis seeks to better understand the ballistic and blast response of CLT panels and to develop evaluation criteria for the use of CLT in temporary military structures. Specific areas of investigation included: 1) experimental testing of the ballistic resistance of CLT panels, conducting in conjunction with U.S. Army laboratories in Aberdeen Proving Grounds, Maryland and Vicksburg, Mississippi; 2) the design, prototyping, and experimental testing of enhanced CLT panels to further improve ballistic performance; 3) a qualitative analysis of CLT panels under ballistic impact resistance mechanisms; 4) the development of a CLT blast analysis tool to predict the elastic response of CLT to blast loadings; and 5) the development of a simplified tool to identify evaluation criteria for temporary military structure material selection, including conventional materials as well as CLT. Specimens in this research consisted of commercially produced Spruce-Pine-Fir CLT as well as Southern Pine CLT specimens fabricated specifically for this research. Ballistic testing of both types of conventional CLT indicate that the material’s inherent penetration resistance is significantly greater than that of dimension lumber and plywood used in current common temporary military structures. The testing shows that current U.S. military design guidelines (UFC 4-023-07), used for determining required wood thickness based on ballistic threat, under predicts the ballistic performance of CLT. From testing and analysis, the thesis develops updated equations for predicting the thickness of CLT required for ballistic protection. A qualitative analysis of ballistic specimens identified local failure modes in the CLT and links the observed damage the anisotropic material properties, grading, and defects in sawn timbers. Enhanced CLT specimens were fabricated using various hardening materials including thin metal plates and gratings, polymer-based armors, and fiber-reinforced epoxy matrix panels. The enhanced CLTs were evaluated based on ease of production, ballistic resistance as compared to conventional CLT, and cost-benefit analysis. The shear analogy method was incorporated into a single-degree-of-freedom blast analysis to predict the response of different types and sizes of CLT panels under blast loads within the elastic regime. The tool was validated using field data from low-level live blast tests and showed good agreement with the field data. Finally, tailored evaluation criteria for comparative assessment of construction materials for use in temporary military structures – considering issues of cost, the logistics of in-theater deployment, energy consumption and force protection were developed and applied through using the AHP decision-making process.
The technique proposed herein, aims to solve the construction site issues related to both the handling and the assembly of cross laminated timber walls (CLT), through an innovative preassembled connection system. This system, which thanks to its being pr...
The Task Group on Combustible Construction is in the process of evaluating a proposed code change request related to buildings of encapsulated mass timber construction (EMTC). As part of the analysis of the code change request, an impact analysis is required that includes a cost-benefit analysis.
Hanscomb was hired to provide a cost-benefit analysis and to compare the estimated value of the following:
1. The cost of constructing a building of mass timber (unprotected) versus a building constructed of encapsulated mass timber (e.g. mass timber protected with a double layer of Type X gypsum board) versus a traditional concrete and steel building.
2. The time to build a building of mass timber construction (unprotected) versus a building of encapsulated mass timber construction versus a traditional concrete and steel building.
3. The annual maintenance costs of building of mass timber construction versus a building of encapsulated mass timber construction versus a traditional concrete and steel building.
For the purposes of this study two sets of conceptual floor plans and elevations have been created:
1. A 12 storey building with a Group C major occupancy (residential) where each storey is 6,000 m2 in floor area.
2. A 12 storey building with a Group D major occupancy (office) where each storey is 7,200 m2 in floor area.
The Canterbury earthquakes in 2010 and 2011 caused significant damage to the Christchurch building stock. However, it is an opportunity to build more comfortable and energy efficient buildings. Previous research suggests a tendency to both under heat and spot heat, meaning that New Zealand dwellings are partly heated and winter indoor temperatures do not always meet the recommendations of the World Health Organization. Those issues are likely to be explained by design deficiency, poor thermal envelope, and limitations of heating systems.
In that context, the thesis investigates the feasibility of building an energy efficient and cost-competitive house in Christchurch. Although capital costs for an energy efficient house are inevitably higher, they are balanced with lower operating costs and improved thermal comfort. The work is supported by a residential building project using Cross Laminated Timber (CLT) panels. This atypical project is compared with a typical New Zealand house (reference building), regarding both energy efficiency and costs.
The current design of the CLT building is discussed according to passive design strategies, and a range of improvements for the building design is proposed. This final design proposal is determined by prioritizing investments in design options having the greatest effect on the building overall energy consumption. Building design features include windows efficiencies, insulation levels, optimized thermal mass, lighting fixture, as well as HVAC and domestic hot water systems options. The improved case for the CLT building is simulated having a total energy consumption of 4,860kWh/year, which corresponds to a remarkable 60% energy savings over the baseline.
The construction cost per floor area is slightly higher for the CLT building, about 2,900$/m² against
2,500$/m² for the timber framed house. But a life cycle cost analysis shows that decreased operating costs makes the CLT house cost-competitive over its lifetime. The thesis suggests that the life cycle cost of the CLT house is 14% less than that of the reference building, while the improved CLT design reaches about 22% costs savings.
The paper reports on the activities of the RILEM technical committee Reinforcement of Timber Elements in Existing Structures. The main objective of the committee is to coordinate the efforts to improve the reinforcement practice of timber structural...