WIND RESISTANT STRUCTURES

 

Winds swirl about our planet. More than most other aspect of nature, wind is both friend and foe. It grants us joys as well as many practical benefits. Yet these life-giving aspects are counterbalanced by fierce assaults on the built environment. Strong winds could cause damage to buildings, bridges, towers, stacks and roof structures, while buffeting of buildings could lead to occupant discomfort which impairs the functionality of structures. Thus, the focus of study of the Centre for Wind Resistant Structures lies in mitigating the hazards resulting from extreme winds.

The design process involved in realizing a wind resistant structure which is safe and functional is described by the wind-load chain (Figure 1). The concept of a chain symbolizes the interaction between disciplines such as meteorology which deals with the characteristics of the wind, aerodynamics which deals with the wind forces on objects due to a given wind flow, and structural mechanics/engineering which deals with the response analysis and design of structural systems and components. The Centre conducts industrially relevant research in this multi-disciplinary field by tapping the expertise in the Departments of Civil Engineering and Mechanical and Production Engineering as well as the Faculty of Architecture. It also collaborates with the Housing & Development Board (HDB), Port of Singapore Authority (PSA), Meteorological Service of Singapore (MSS) and Commonwealth Scientific Institute & Research Organisation, Australia (CSIRO).

Although a great deal is known about how to mitigate wind damage, much is yet to be learnt. Sustained research is needed in the areas of defining wind loads, determining more economical ways to resist these loads and finding ways to implement solutions in practice. This is all the more so when a new generation of structures which are much larger and taller are feasible due to advances in the manufacture of high-strength materials, computational techniques and construction technology. Thus the Centre is adopting the following methodologies in order to advance the overall knowledge base:

  1. Physical modelling of wind-structure interaction
  2. Analytical/numerical modelling taking advantage of powerful computing capability
  3. Full-scale field measurements to verify predictions made by physical and/or numerical modelling.

To provide better panoramic views and create open spaces at ground level, the HDB is building 30-storey blocks. Furthermore, in areas where there are no severe height restraints, taller blocks are envisaged. The heights of such buildings are in the range where wind loads may be substantial. Moreover, when HDB blocks are built as a cluster of tall structures, the mean loads are reduced by the presence of surrounding buildings, while the fluctuating loads are increased due to higher turbulence. Thus to produce a cost-effective design, a methodology for assessing wind loads and the demand on structural strength is needed. With this in mind, the Centre carries out physical modelling in small-scale and large-scale tests. Structural models are tested in the boundary layer wind tunnel for structural loads and responses. The Centre has developed a technique to fabricate aeroelastic models which simulate the typical mode of vibration of buildings more accurately. Using such models, dynamic loads and responses may be assessed more correctly. On the other hand, by means of the large scale pseudo-dynamic testing facility, the effectiveness of slot-bolted connections in dissipating the wind energy has been investigated. Such connections lower the demand on the strength of structural members and hence reduce the cost of wind resistant structures.

The regions of ASEAN and East Asia are experiencing rapid economic growth and this has resulted in the construction of massive infrastructure which includes larger and/or taller structures. The wind induced motion in such structures is relatively large and the motion causes the loads that the structure must resist to increase above those induced by the wind alone. The motion can be reduced either by increasing the stiffness or by dissipating energy through damping. Using analytical/numerical methodology, the Centre has investigated the vibration control of wind resistant structures through (a) judicial positioning of structural elements which increases the stiffness, and (b) passive, and a combination of passive and active dampers.

Field measurement is necessary to validate the physical or numerical modelling. Complexities in field measurements arise from the surrounding topography, terrain, wind climate, unpredictable nature of wind and the complicated structural system of buildings. However, new technologies in instrumentation provide opportunities in field measurements that were not available previously. Solid-state electronics, remote sensing devices, and computerized data acquisition systems permit reliable and detailed measurements. The Centre is conducting long-term measurements on high-rise buildings. The OUB Centre has been selected as one of the buildings to provide the database. The measurements on buildings will supplement data on wind records and profile from the Meteorological Service of Singapore with a view towards forming an appropriate wind loading standard for Singapore.

The Centre is also actively involved in developing a general loading standard for design and construction of buildings in countries belonging to Asia Pacific Economic Corporation (APEC), as this would mitigate the problem of the trade barriers and promote the regionalisation of local industry. In this regard, the Centre is collaborating with the CSIRO (Australia) in organising seminars and workshops on the harmonisation of regional wind codes. Some other research work conducted by the Centre is described in the following feature articles of this issue.

 

Figure 2 Aeroelastic model for dynamic response measurements in a wind tunnel

Figure 3 Slot-bolted connection for energy dissipation through friction

Figure 4 Wireless data logging system for field measurement of tall buildings

 

 

Contact Persons:

 

 

A/Prof T Balendra, Director, Centre for Wind Resistant Structures

(Tel: 874-2159, Fax: 779-1635, Email: cvebalen@nus.edu.sg)