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PRACTICAL APPLICATIONS FOR CONSTRUCTION AND THE BUILT ENVIRONMENT

Issue No. 96 Also at www.innovationandresearchfocus.org.uk February 2014

Innovation & ResearchIN THIS ISSUE

1www.innovationandresearchfocus.org.uk Innovation & Research Focus Issue 96 FEBRUARY 2014

AWARDSMacRobert Award construction fi nalist 5 2014 Structural Research Awards 6

CONSTRUCTION2050 Group: ‘A voice for future generations’ 4MacRobert Award construction fi nalist 5

DRAINAGEADAPTing to optimise drainage systems 7

ENERGY & CARBONInnovation needs for a low carbon future 3Performance of thermal break materials 6Thermal mass in low-energy UK housing 8

ENVIRONMENT & HEALTHNanotechnology – answer or problem? 5

FUNDING2014 Structural Research Awards 6Need some research funding? 2

GEOTECHNICSImpact of fl uid mud on ports & navigation 2

HOUSINGThermal mass in low-energy UK housing 8

KNOWLEDGE SHARING2050 Group: ‘A voice for future generations’ 4

MATERIALSNanotechnology – answer or problem? 5Performance of thermal break materials 6

Assessing building façade access loadsAccess to building façades for maintenance and cleaning may be by roped access, suspended cradle, hydraulic access platf orm or a mobile elevati ng work platf orm (MEWP). It is the damage caused by access that triggers considerati on for potenti al hazards.

Major damage resulting from access is not a frequent occurrence but it may present a hazard from

falling materials, and repair costs may be disproportionate to the damage caused. It is therefore always important to consider impact loads when designing façades.

The loads associated with the different means of access are of very different magnitude and frequency of occurrence. Roped access loads are the lowest but are inevitable and may be damaging. Collisions from hydraulic platforms can occur as a result of operator or system error and are more frequent than might be anticipated. Cradles are less easy to control precisely and are susceptible to wind induced collisions.

It is important to distinguish between safety and serviceability design criteria. Safety loads will depend on methods of working and degree of exposure of the public to falling materials. Many engineers make simple calculations of impact loads that are far in excess of those that may occur. The alternative of impact testing with a cradle and full scale façade mock-up is normally prohibitively expensive.

Calculation of impact loads using time stepping methods allows for the transient nature of the wind and the inertia of the cradle to be taken into account. This approach shows that the predicted impact loads are far lower than often predicted and that lighter weight cradles are potentially as damaging as heavier cradles. It also shows that skew collisions are no worse than collisions of the cradle parallel to the wall.

A dominant factor affecting impact loads is the length of the suspension cable between the cradle and the hoist or an intermediate anchor. There are always confl icts between ease of operation and the use of frequent anchor points. Similarly, use of the cradle may be restricted when winds reach a certain level. However, this has an effect not only on productivity but also on planning of maintenance and cleaning operations.

It follows from this analysis that the method of access, and the maintenance and

cleaning operations, have to be considered at an early stage of façade design. The client and/or operator have to be involved in these discussions along with the manufacturer of the access equipment and the façade engineer. Most plain building façades can be designed to resist cradle impact loads and other access loads in terms of safety. However, façades with projecting fi ns and shading devices present more of a problem and re-engineering a design may be diffi cult and/or expensive. Design of façades for serviceability often requires the substitution of more robust materials.

CWCT is publishing Technical Notes on the selection of appropriate access equipment and the impact loads for which the building envelope should then be designed. This includes the process of access design and the timely exchange of information to develop appropriate strategies for design and adequately robust façades.

For further information please contact Brenda Apted, Centre for Window & Cladding Technology at the University of Bath (01225 386506; E-mail: absbaa@bath.ac.uk).

A typical articulated cradle