Ascent, a 25 story residential tower located in Milwaukee, WI (USA), will become the tallest timber building in the world upon completion. This paper discusses the project's structural system, permit process, groundbreaking project specific testing, and several of the challenges the team overcame, all of which open the door to future Mass Timber projects; particularly in the United States.
In response to the global drive towards sustainable construction, CLT has emerged as a competitive alternative to other construction materials. CLT buildings taller than 10-storeys and CLT buildings in regions of moderate to high seismicity would be subject to higher lateral loads due to wind and earthquakes than CLT buildings which have already been completed. The lack of structural design codes and limited literature regarding the performance of CLT buildings under lateral loading are barriers to the adoption of CLT for buildings which could experience high lateral loading. Previous research into the behaviour of CLT buildings under lateral loading has involved testing of building components. These studies have generally been limited to testing wall systems and connections which replicate configurations at ground floor storeys in buildings no taller than three storeys. Consequently, to develop the understanding of the performance of multi-storey CLT buildings under lateral loading, the performance of wall systems and connections which replicate conditions of those in above ground floor storeys in buildings taller than three storeys were experimentally investigated. The testing of typical CLT connections involved testing eighteen configurations under cyclic loading in shear and tension. The results of this experimental investigation highlighted the need for capacity-based design of CLT connections to prevent brittle failure. It was found that both hold down and angle bracket connections have strength and stiffness in shear and tension and by considering the strength of the connections in both directions, more economical design of CLT buildings could be achieved. The testing of CLT wall systems involved testing three CLT wall systems with identical configurations under monotonic lateral load and constant vertical load, with vertical loads replicating gravity loads at storeys within a 10-storey CLT building. The results show that vertical load has a significant influence on wall system behaviour; varying the vertical load was found to vary the contribution of deformation mechanisms to global behaviour within the elastic region, reinforcing the need to consider connection design at each individual storey. As there are still no structural design codes for CLT buildings, the accuracy of analytical methods presented within the literature for predicting the behaviour of CLT connections and wall systems under lateral loading was assessed. It was found that the analytical methods for both connections and wall systems are highly inaccurate and do not reflect experimentally observed behaviour.
International Structural Engineering and Construction Conference
Proceedings of International Structural Engineering and Construction
The main objective of this paper is to study the structural performance of a high-rise
structure when alternative lightweight material known as cross-laminated timber was
used as a slab in floor system in lieu of conventional reinforced concrete slab. A
numerical case study was conducted using a highly irregular RC frame building with its
two 60-story towers joined at the top. Three major analyses were considered. First,
modeling and analyzing the building with an RC slab was conducted to determine the
design reference. Second, substituting the RC slab with the CLT slab was performed
using the same building skeleton. Third, redesigning and optimizing the building
skeleton with that CLT to observe skeleton material saving obtained using the same
structural performance criteria. Major lateral loads applicable in the Eastern Province
of Saudi Arabia were inputted. Strengths and serviceability requirements for floor
diaphragm and lateral load resisting system were checked first before performing a
comparative analysis between traditional RC and CLT slabs as floor diaphragm. The
structural performance criteria to be used for comparative study between RC and CLT
slabs included total drift, inter-story drift due to lateral loads, and base reactions.
Structural periods and acceleration responses for each floor were investigated and
contrasted with the existing building code. The foundation demand was also
investigated based on the structural weight and reactions generated from the RC and
CLT floor systems.
Project contact is Frank Lam at the University of British Columbia
The objective of this project is to develop a large span timber-based composite floor system for the construction of highrise office buildings. This prefabricated floor system could span over 10 m under regular office occupation load, and its use will expedite the construction significantly, converting to multi-million financial savings in a typical 40+ story project, besides the impact on reducing carbon footprint and enhancing living experience.
This paper reflects on the structural design of Haut; a 21-storey high-end residential development in Amsterdam, the Netherlands. Construction started in 2019 and is in progress at the time of writing. Upon completion in 2021, Haut will be the first residential building in the Netherlands to achieve a 'BREEAM-outstanding' classification. The building will reach a height of 73 m, making it the highest timber structure in the Netherlands. It contains some 14.500 of predominantly residential functions. It features a hybrid concrete-timber stability system and concrete-timber floor panels. This paper describes the concepts behind the structural design for Haut and will touch upon the main challenges that have arisen from the specific combination of characteristics of the project. The paper describes the design of the stability system and -floor system, the analysis of differential movements between concrete and timber structures and wind vibrations. The paper aims to show how the design team has met these specific challenges by implementing a holistic design approach and integrating market knowledge at an early stage of the design.
Project contact is Solomon Tesfamariam at the University of British Columbia
This project is aimed at developing a resilient timber buildings for high-rise and mid-rise structures using innovative energy dissipators. To improve the seismic performance of the structure, resiliency has become an important factor. Resiliency of the CLT building, in this proposal, is ensured by using novel hybrid building and innovative energy dissipator connectors. This will be undertaken within resilience-based design framework to enable building owners make an informed decision on the potential emergencies and downtime, and mitigate it at the design level. Indeed, this design framework is a departure from the current collapse prevention performance limit objective that will make tall timber building attractive to builders and owners. Furthermore, the use of innovative energy dissipators and structural systems can push the building height beyond the 12-storey proposed in the 2020 NBC.
1. Select ground motions suitable for NBC 2015/2020
2. Performance-based design mid-rise building incorporating energy dissipator
3. Damped outrigger building
4. Coupled walls with distributed dampers
Use of timber as a construction material has entered a period of renaissance since the development of high-performance engineered wood products, enabling larger and taller buildings to be built. In addition, due to substantial contribution of the building sector to global energy use, greenhouse gas emissions and waste production, sustainable solutions are needed, for which timber has shown a great potential as a sustainable, resilient and renewable building alternative, not only for single family homes but also for mid-rise and high-rise buildings. Both recent technological developments in timber engineering and exponentially increased use of engineered wood products and wood composites reflect in deficiency of current timber codes and standards. This paper presents an overview of some of the current challenges and emerging trends in the field of seismic design of timber buildings. Currently existing building codes and the development of new generation of European building codes are presented. Ongoing studies on a variety topics within seismic timber engineering are presented, including tall timber and hybrid buildings, composites with timber and seismic retrofitting with timber. Crucial challenges, key research needs and opportunities are addressed and critically discussed.
This research was conducted to discover how the U.S. building construction and forest products sectors could benefit from the development of tall, cross-laminated (CLT) and mass timber buildings. Barriers that may restrict such development were also investigated. The primary benefits were discovered to be eco-performance and job creation. Code restrictions and material performance misconceptions were found to be the largest obstacles. Case studies of Treet, Tamedia, and the WIDC were conducted to demonstrate the benefits of tall wood buildings and the various paths around potential barriers. Opportunities for tall wood buildings in the U.S. are also discussed. This research discovered that a tall wood movement is gathering momentum in the U.S. To fully realize this potential, accurate information regarding the use of wood and the performance capacities of mass timber systems needs to be disseminated. Co-operation between academia and industry will also be necessary.