Building Materials get Tougher... and Smarter
25 September 2009
Rapidly deployable aircraft shelter. Blast and explosion field tests as well as bullet penetration tests have been conducted by the team on the materials for the shelter.
Prof Richard Liew(picture) and his team have been awarded the 3rd Hangai Medal and Prize in 2005 by International Association of Shell and Spatial Structures for best paper on deployable structures.
CLIMATE CHANGE poses complex challenges for engineers. Smart and sustainable solutions are needed for a better tomorrow. To meet such challenges, a team at the Department of Civil Engineering led by Prof Richard Liew has come out with novel solutions. Their award-winning deployable structural system developed in NUS has been further developed into a new mobile solar façade system which promises to supply energy for day lighting of buildings by up to 50 per cent. It will also shave off a third of total cost on photovoltaic (PV) panels.
With current interest in solar energy as a clean energy source, PV technology development for building-integrated applications has garnered a lot of interest. Buildings designed to integrate with PV systems is a smart solution for urbanisation. Prof Liew who is also the Programme Director for Hazards, Risks and Mitigation said: "Solar energy for residential and commercial buildings will solve the problem of conventional fuel-based energy shortage. Once installed, building facades and roofs provide large surface areas which can yield results quickly."
The team's innovations in this area include mobile solar panels -- smart panels equipped with sensors and able to move to the best strategic position to harvest energy from the sun. Another invention, their novel Steel-Concrete-Steel (SCS) "sandwich" system is superior to conventional stiffened steel plate construction in terms of impact and fatigue performance. Feasibility study done by the team has demonstrated that it can be used as an alternative to conventional steel structures, being cost effective as well as environmental-friendly. The system is particularly suitable for applications where there is a need for high structural stiffness and extreme loading. One example of marine applications is the oil tanker, where collision and grounding may cause catastrophic impact on the environment.
"Apart from servicing as heavy duty deck on offshore platform, the system can also function as a caisson to protect offshore platform from moving ice," said Prof. Liew.
SCS sandwich panels are so called because they consist of a concrete core sandwiched between two steel plates which are connected by special J-hook connectors. The core is made of ultra-lightweight concrete with density less than 1450 kg/m3. To enhance the bond strength between steel and concrete, expanded metal sheets are welded to the steel plates, forming a textured interface. This method also increases the load-carrying capacity of the panels. Compared to conventional methods to enhance the static strength of steel-concrete composites, this method achieves the same result with only a slight increase in the overall weight of the materials. The team has filed a provisional US patent for the novel shear connections and the high performing ultra-lightweight concrete materials for the core.
The team also discovered that curved sandwiches enable longer span length for the same loading, being able to resist more loads with less displacement for the same span length.
"Currently, we are researching the bond enhancement comparisons among three kinds of curved sandwich panels -- the normal curved sandwich panels, curved panels with headed shear studs embedded in the concrete core and curved panels with J-hook connectors. We have an ongoing test plan to investigate the performance of these panels under static and simulated ice impact loadings," Prof Liew explained.
Deployable protective structural systems
Being lightweight but strong and tough, sandwich panels are extremely suitable for the construction of deployable protective shelters. The team has developed rapidly deployable protective shelters for aircrafts. They have also designed and engineered a shelter which withstand conventional as well as nuclear weapons. Housing up to 15 people, the shelter can be collapsed into a compact form and hence be transported easily.
"We are developing smarter and tougher alternatives to replace the conventional systems which use wood and steel materials. The lightness will enable easy handling and transportation of the structural component and modules. They need to achieve a weight reduction of at least 40 per cent compared to steel materials in order to be effective," said Prof Liew.
The team has been designing and developing such composite materials which can withstand blast of up to equivalent of 100kg TNT or an MK 82 GP bomb at 5m, earthquakes of aiming up to level 5 of Richter scale and other extreme loads such as vehicular and wave impact.
The teams will be seeking funding to construct full prototypes of deployable protective shelters for aircrafts, emergency shelters for protection of personnel and equipment.