Building Structures

Structural Resiliance

Terrorism is an ongoing risk in the UK and overseas, and with September marking the 10th year anniversary of the terrorist attacks on the US’ World Trade Center and the Pentagon, national security remains high on the country’s agenda. Although UK government counter-terrorism advice has historically focused mainly on crowded places, which remain highly attractive targets, other places at risk include iconic buildings, government, military and diplomatic installations, infrastructure sites, and any site neighbouring these.

Assess the risk level
The UK is a world leader with a body of growing expertise in creating resilient buildings. When putting together an effective security strategy that looks at making a building blast resistant, the level of protection should vary to suit the risk level of the facility. There are many ways in which security and site management concerns can be integrated with counter terrorism, and where new measures are necessary they can often be designed with this dual purpose in mind.

The starting point of counter terrorism design applied to public buildings should always be a risk assessment, to understand the overall risk profile of the activities and organisations that will be housed in a facility and of the facility environs. It is important to engage with relevant stakeholders as early in the design process as possible to establish to what extent, if any, these enhanced security measures are necessary.

Keep threats at a distance
Improvised explosives devices (IEDs) are the dominant terrorist threat to buildings and their occupants, and can be effectively mitigated by keeping them at a distance. Hostile Vehicle Mitigation Measures can be critical in maintaining the maximum stand-off from large IEDs. Traffic management and parking options with static barriers can eliminate or reduce the need for active barrier systems that can be breached by deception or duress, even if they are designed to resist penetration or encroachment. Static barriers do not need to be intrusive, particularly in new developments. Creative use of hard landscaping and water features can in many cases be designed to prevent vehicle access while remaining aesthetically pleasing.

Area based approaches can also be very effective in counter terrorism protection for both the public realm and the associated buildings and facilities. The pedestrianisation of a square, for example, by using robust street furniture as vehicle barriers can protect both crowded public places and private buildings. Similarly, systems designed for congestion control can be used to reduce the number of active control points required around a high risk area, and allow resources to be concentrated.

Moreover, access control measures, whether at active vehicle barriers, at reception facilities or at rear and escape doors are a key defence to keep IEDs away from and outside buildings. These defences can be strengthened by technical measures such as intruder alarms, surveillance CCTV and automated number plate recognition.

Consider the structure
From a structural point of view, glass facades often require careful analysis because of the extensive and severe injuries that can be caused by glass fragments in case of a blast.

There are two possible solutions to the risk of glass fragments caused by blast. The first is to design the glazing not to break. However, this leads to very thick glass that causes very high reactions and requires very strong frames and structural supports. This results in uneconomic facades that are not a realistic option for most buildings.

The alternative solution is to design glazing that retains the glass fragments after cracking. For new construction, this can best be provided using a PVB laminated glass inner leaf, adequately anchored to the frame. Similar effects can be obtained by applying anti-shatter film to the inside of existing glazing, although usually to a lower level of protection.

Blast design is not fully standardised, so solutions tend to be site or client specific, although some standards do exist, e.g. recipe glazing designs for normal risk levels to UK government buildings. For more severe blast levels, blast testing or dynamic analysis informed by blast testing is the norm, using laminated glass of appropriate make-up anchored into enhanced frames.

Seek advice
General advice is available from government sources and expertise from specialist can also be sought to ensure a meticulous and appropriate assessment is undertaken.

Counter Terrorism Security Advisors (CTSA) in the various UK police forces can give initial advice on risk levels, and provide general advice on practical mitigation measures that are preferred for medium and low risk sites, such as most public buildings. Moreover, the Centre for the Protection of National Infrastructure (CPNI) is a government authority which provides protective security advice to businesses and organisations across the national infrastructure.

Taking on board a reputable and experienced security consultancy is also essential when planning counter terrorism measures for buildings. Members of the BSIA Security Consultancy section meet strict quality criteria, and can provide expert advice and assistance from the initial risk assessment through design considerations and solutions, to design detailing and testing of solutions.

For more information
www.bsia.co.uk/consultancies