The Use of Timber in a Temporary Multi-storey Car Park

Abstract

Problem definition: In the car park industry, a new trend has emerged, shifting the demand for parking from permanent one-of-a-kind parking structures towards temporary modular structures (Drenth, 2020). Meanwhile, the building industry faces a transition into a more sustainable industry. This requires rethinking of the design process, taking into account possible reuse of a building or its elements as well as potential use of different materials. Timber is a renewable material and as a result of developments in timber engineering, now allows the construction of taller and larger structures. Given these trends and challenges, the objective of this thesis is to provide a structural system proof of concept for a temporary multi-storey car park, using timber as primary structural material.
Approach: A broad literature study provides background information on the various relevant topics and is followed by a refinement of the objective, substantiated by two sub-studies. This has resulted in two sub-goals: the minimization of total deck height (< 700 mm) and minimization of the structural systems weight (column load < 1,000 kN). A proof of concept is developed through a parametric study with structural validation into four main design variants (consisting of a deck and framing system), for which the effect of altering four geometric parameters (parking deck span, use of struts, distance between columns in transverse direction and minimum distance between joists) on these sub-goals is studied. Furthermore, a sensitivity analysis is performed on the effect of altering the requirements concerning fire-safety, vibrations and deflections on the deck height and weight. Finally, the proof of concept’s performance is compared to five alternative modular and/or timber car park concepts in a case study.
Evaluation: It is concluded, that design variants using long-span deck systems result in a relatively small deck height, but high self-weight. A CLT rib deck should be applied under “standard” assessment criteria, but significant reductions in deck height (31%) and weight (49%) can be achieved by using LVL rib decks when vibrations are not considered and deformation limits are increased. The total deck height of design variants with short-span decks, which use solid LVL panels, highly depends on the supporting framing system, but its self-weight is roughly halve of the long-span design variants. The effect of alternative assessment criteria on design variants with short-span decks is rather limited. It is concluded that the use of struts significantly reduces the total deck height (17-30%) and structures weight (5-11%) and a transverse column distance of a single parking bay width is preferred. The distance between joists is of less relevance, but a bigger parking deck span increases both deck height and total weight.
The resulting proof of concept consists out of a short-span solid LVL deck system, which spans two times 2.5 m (single parking bay width). It is supported by glulam main girders, spanning the entire parking deck, which are simply supported by a set of columns at a transverse distance of 2.5 m and are additionally supported by slanted struts between the columns and main girders.

The results from the case study show, that the total deck height of the proof of concept (666 mm) is smaller that the sub-goal of 700 mm and comparable to alternatives with decks made of steel, concrete and GFRP. Furthermore it is 40% thinner than the alternative in timber as a result of the use of LVL and struts. In terms of weight, the use of timber is much lighter than using concrete decks (<25%) and only 17% heavier than the extremely lightweight GFRP decks. Furthermore, it results in the smallest loads on the foundation (678 kN which is smaller than the sub-goal of 1,000 kN). A first extremely simplified durability analysis on amounts of embodied carbon in the main structural elements indicates timber has significantly lower amounts of embodied carbon in comparison to the alternative concepts.
Implications: Based on the results presented, it is concluded that timber is applicable for almost all main structural elements of a temporary and modular multi-storey car park. The case study has shown that the proof of concept can compete with alternative modular car park concepts in terms of deck height and outperforms most alternatives in terms of the structures weight. It is also indicated, that timber has the potential to significantly improve the performance of a structure in terms of sustainability.
For future research, it is advised to further develop the proof of concept, focussing on the connections and durability risks and study the incorporation of circular design strategies into the design and construction process of the proof of concept. Furthermore, alternative assessment criteria should be validated. Finally, it is advised to study the potential use of other innovative sustainable building materials like BauBuche and make a detailed LCA study assessing the performance on sustainability.