BUILDING INFORMATION MODELLING Part 4
Clash detection has long since been the buzz word in BIM. This is because it is possible to put a value on the savings made from eliminating problems found during a clash detection review. According to the report by the contractor “use of the 3D digital model, prevented 1200 collision of steel elements and sped up steel erection”. On the Benjamin D. Hall, Washington University, they estimated 1500 potential clashes were eliminated. While CURT indicated clash detection was one of the most promising aspects of BIM, particularly in pharmaceutical and manufacturing plants with heavy mechanical and electrical elements.
The Homan High speed railway project found clash detection invaluable. Whilst the Birds Nest (National Stadium Beijing 2008 Olympics) assessed over 2400 nodes. As a teaching tool it has proved invaluable in allowing students see where mistakes are being made without having to spend wasteful time trawling through countless 2D drawings instead of productively learning. Clash detection can be broken into three categories or three types of clashes. 1) Hard clash. 2) Soft Clash/Clearance Clash. 3) 4D/Workflow Clash.
A hard clash is simply when two objects occupy the same space. For example, a pipe cannot go through a wall without there first being and opening. Rule based algorithms can be used to allow automatic solutions too many hard clashes. Clash detections can be run against sub-sets of the model. One could run mechanical ducting against just ceilings or just electrical sets or walls against steel structure etc.
Soft clashes refer to allowable tolerances or space. Buffer zones between components. These spatial allowances may be to provide space for ongoing maintenance, future expansion, safety codes or expansion and contraction among other reasons.
4D/Workflow clashes refer clashes in scheduling work crews, equipment/material fabrication delivery clashes and other timeline issues.
BIM has the ability to produce full and accurate quantities for any components built in the 3D model. Each component is made up of a specific ingredient. This intelligent model allows a clear breakdown of very specific quantities to be produced. (Tulke, Nour and Beucke 2008) indicated that 4D software at the time could not handle much of this data. They were simply a basic link to the component but could not use quantity, cost or geometric data etc. Also, software was very expensive at the time.
However, even accurate quantities gave considerable help in producing budgets and time estimates based on productivity rates. If the model changed, so to would the quantities. This eliminated the need for time consuming remeasure. Unfortunately, a change in the model did not create an automatic link to change the measures in the chosen quantity surveying software or the scheduling software. These still had to be extracted from the 3D software and inputted manually. The confidence in the quantities allowed far more certainty in budget estimates and less concern about the requirement of adding contingency. It also allowed for far more confidence in procurement.
“The spirit of BIM is collaborative and integrated by definition and goes unrealised when a design team creates a BIM without planning, scheduling and cost professionals contributing to the model in 4D and 5D”(McCuen 2008). How far one goes with BIM is often down to the maturity level of the team and its respective parts. To use fully integrated 3D, 4D and 5D are still very uncommon. This is down to software costs and educational restrictions. This applies to the US as well as the UK and Ireland. The certainty of quantities allow several different models to be assessed for the most cost effective solutions prior to construction.
Change in the construction industry has always been slow due to its conservative nature. Olatunji et al (2010) also identified the potential conflict of interest professionals might have with the use of BIM. This is particularly evident when it comes to the quantity surveying practice. Using accurate 3D BIM models produced by architects, engineers etc, means that a schedule of quantities can be produced at the push of a button. Previously a quantity surveyor could spend very long periods of time physically measuring and taking of quantities from 2D drawings. The construction industry has not historically embraced IT or technological advancements nearly as quickly as most other sectors in the economy. In Ireland we have long since listened to the mantra of how productive our construction industry is, but this is only in relation or comparison to construction sectors in other jurisdictions. In fact, construction productivity declined since the 1960’s in the US and most other developed countries whilst other sectors showed dramatic growth in productivity. Many analysts place these results squarely at the construction industries lack of integration, inability to embrace IT advancements, low off site fabrication, fragmentation on professional services and protectionist stances from vested interests. Quantity surveyors are aware that BIM could reduce their workload significantly. However, they need to emphasis and concentrate on the other services they provide. They are not simply a profession that does basic take off measurements but rather give other services such as contractual advice, financial advice, budgeting and project management among other areas of expertise.
Despite BIM’s accurate quantity measurement ability, there remains the issue of differing standard methods of measurement. In Ireland we generally use a version of ARM (Agreed Rules of Measurement) whilst in the UK they use SSM (standard Rules of Measurement) or for civil works they use CESSM. In the US and Australia they use other methods of measurement. As noted by Olatunji et al (2010), it is likely that software companies will only develop measurement software to suit the extraction of BIM quantities in the method of measurements in the largest markets. This would almost certainly not include Ireland which has ARM as its own isolated method. It would therefore be advisable for the construction industry to liaise with their international counterparts to produce a common means of measurement which will allow us utilise the BIM software’s.
Finally, as already discussed, taking off quantities is generally a long, tedious and laboursome process. Whilst it is an analytical and methodical task, it does not require highly intellectual skills. During education, it is a process which requires long periods of time when this may be better served on more complex value adding training and education.
However, previously progress tracking and earned value analysis was a manual task which was difficult to do accurately in the construction industry. It required someone to do an assessment of the percentage work complete on each activity. Without physically measuring each task, it was impossible to do this accurately and even if estimating roughly the progress of each task, it still required someone to visit site and make this assessment of each of these tasks. On a large site, this would take a considerable length of time and potentially not be accurate enough to flag poor performances in schedule or budget. Thankfully, although not widely available yet, much work has been done in automating progress tracking. Turkan et al (2012) carried out studies on integrating many current technologies. They carried out the tests on the technology in the Engineering V building in the University of Waterloo which showed that automated tracking met or exceeded the current methods for accuracy. There are currently several technologies which can help in carrying out automated tracking; these include LADAR (laser detection and ranging), GPS, Ultra wide band tags and photogrammetry. Many sensing technologies do not naturally produce project oriented data. However, with the correct mix of technologies it is possible to create 3d data stored as dense cloud points. This makes it possible to scan rooms, and update the 3D and 4D models. Laser scanning also offers the ability to quickly validate construction work carried out in relation to what was expected or designed. This can obviously greatly increase quality as this validation will force contractors to ensure the construction is carried out as per the drawings as it will be noted in progress reports.
It has also become apparent that the critical path method of scheduling is becoming less utilised in relation to 4D scheduling. Whilst most BIM oriented 4D scheduling packages still offer CPM Gantt style software, most now also include the location based scheduling software Line of balance/Flowline scheduling method. The argument has been that CPM focuses too much on the duration of the project and does not take into consideration enough the flow of resources. Location based scheduling (LBS) is a combination of CPM and linear scheduling methods. This method is perhaps becoming more prevalent in other countries rather than Ireland due to the high rise construction which takes place in them. Location based scheduling is particularly useful for repetitive tasks in different locations. Like floor levels.