Impacts of IBS score regulations of CIDB on the concrete volumes required for building projects in Malaysia

Sami Mustafa M. E. Ahmed, Noor Amila Wan Abdullah Zawawi and Zulkipli B. Ghazali

Improvement of construction industry will contribute to the economy of Malaysia because it is one of the five sectors used to calculate the national GDP.

This fact is encouraging the Construction Industry Development Board (CIDB) of Malaysia to prepare many development plans like Roadmap 2003-2010, CIMP 2006 2015, and Roadmap 2011-2015.

Adoption of the Industrialized Building System (IBS) is the step stone for all these plans. CIDB has created an indicator to assess the degree on industrialization for applied building system; IBS score. Furthermore, CIDB has specified the minimum values of this score for the building projects of government and private sector.

This paper discusses the effects of adjusting these values on the structural design of an office building .

The CIDB method of calculating the IBS score, the moment distribution method of structural analysis and BS8110 code of design will be used to analyze the selected case study.

C3 400 C2 425 425 C2 Beam1 C2 425 C2 425 C2 250 250 C2 Beam6 C2 C2 400 400 C2 Beam2 C2 400 C3 450 D C3 1 C2 C2 C2 2 C1 C1 C1 C1 Beam4 Beam4 C1 C1 C1 C1 C2 Beam1 3 C2 4 C2 C1 C2 C1 C2 C2 C1 C1 C2 C1 Beam5 C1 C2 5 6 7 6: Construction joint 8 C1 C2 Beam5 C1 C2 9 C1 C2 300 C C1 C2 B 450 C2 10 C3 11 A

1. Column : the section of C1 is 25×50 cm and of C2 and C3 is 25×45cm. The reinforcement for all types is 6φ16mm and St.R8@150mm. C2 and C3 are the same in super structure level but their short columns have different sections.

25 25 25 2. Beams : sections of all beams are the same; 250×500 cm. The average reinforcement for all beams is 8φ16mm (with consideration of cutoff points) and St.R8@150mm. Section (a) is used at the middle and near support of beams equal or less than 3m. Section (b) is used at the middle and (c) near the support for the other beams.

25 25 25 3. Slabs : the thickness of slab is 130mm. The reinforcement of top and bottom is φ10@150 b/w.

(Columns)

section of 300×300mm with reinforcement of 4φ20mm and St.R10@225 mm is found to be suitable for all columns after the structural analysis is revised.

(Slabs)

For span of 5m length, a half precast slab of depth 7.5cm and to be topped up by concrete of 12.5cm depth; the total depth will be 20cm. The main reinforcement for top and bottom layers is φ10-100c/c, and the secondary for both layers is φ10-250c/c. The width of each panel is either 600 or 1200 or 2400 mm.

(Beams)

 For A and D from 1 to 6, a section of 300×500 with 7φ16 mm and St.R10@200 is proposed.  For A and D from 6 to 11, a section of 300×550 with 6φ16 and St.R10@200 is sufficient. For B and C from 1 to 6, a section of 350×500 with 8φ16 and St.R10@150 is considered. For B and C from 6 to 11, a section of 350×500 with 7φ16 and St.R10@ 150 is suggested. For external (1 & 11) and construction joint (6) beams, a section of 350×450 with 7φ160 and St.R10@250 is proposed for the length from A to B and from C to D.  A section of 350×600 with 5φ12 & 2φ16 and St.R10@200 is considered for the length from B to C.  For other beams in this direction from A to B and C to D, a section of 300×450 with 7φ16 and St.R10@250 is proposed, and  A section of 300×550 with 4φ12 & 2φ16 and St.R10@200 is found to be sufficient for the length from B to C.

(Walls)

A block could be considered as an alternative for the brick and it will increase the IBS score.

IBS score reflects the degree of industrialization of composite building system.

IBS score = S 1 +S 2 +S 3 Where: S 1 = 50×Ʃ (Q s /Q st ) ×F s vertical).

;Fs factor of the structural system from Table 1 S 2 = 20×Ʃ (W s /W st )×F w S 3 ; Fw is factor of the wall system from Table 2 is factor for compatability with MS1064 and repeatioions (floor height, horizontal and Q s /Q st : the percentage of the construction area of which a particular system is used; out of the total construction area of the building include roof Q w /Q wt : the ratio of a particular wall system (external or internal) used out of the total wall length of the building

Table 1 Factor of structural system (Fs)

Beam system Column system precast Floor system RFS* TFS* No-floor Precast Precast Precast RFS* TFS* RFS* TFS* Precast RFS* TFS* RFS* TFS* Precast Precast 1.0

0.9

0.8

0.7

0.6

0.9

0.8

There are four types of roof considered;  Prefab timber roof truss (PTR, Fs=1.0),  Prefab metal roof truss (PMR, Fs=1.0),  Pre-cut metal roof truss (PCM, Fs=0.5) and  Timber roof trusses (TMT, Fs=0.0). 0.7

0.6

0.5

0.5

0.3

0.6

0.5

0.6

0.5

0.4

0.3

0.0

0.5

0.4

1.0

0.8

0.7

0.6

0.0

0.8

0.7

Table 2 Factor of wall system (Fw)

No 1 2 3 4 5 6 Wall System Precast concrete panel (PCP) In-situ concrete with RFS* In-situ concrete with TFS* Block-work system (BWS) Pre-assemble brick wall/ block wall (PBB) Common brick wall (CBW) Fw 1.0

0.5

0.0

0.5

1.0

0.0

Table 3 compatability with MS1064 and repeatioion (S3)

Description Unit IBS score Percentage of usage 50% to <75% 75% to <=100% 1 2 3 Utilization of standard components based on MS 1064 1 Beams Nos 2 4 2 Columns Nos 2 4 3 4 5 6 Walls Slabs Doors Windows Repetition of structural Layout m M 2 Nos Nos 2 2 2 2 4 4 4 4 1 a) For building > 2 storeys Floor to floor height Nos Vertical repetition Nos Horizontal repetition Nos b) For building 1 or 2 storeys Horizontal repetition Nos 1 1 1 3 2 2 2 6

Switching from conventional columns which require 5.62 m3 of concrete per meter length to equivalent precast columns of concrete volume of 4.32m

3 per meter length will reduce the volume of concrete by 1.305 m 3 per meter length per each floor.

The concrete volume for conventional beams= 0.25×0.5× (4× (23+17) +12×12) =43 m 3 per floor.

The concrete used for IBS beams= 23×2×(0.3×0.5+0.35×0.5)+17×2×(0.3×0.55+ 0.35×0.5)+ 9×4×0.3×0.45+3×4×0.35×0.6+ 9×8×0.3×0.45+3×8×0.3×0.55 =47.57 m 3 per floor.

The total increase in concrete volume due to switching from conventional to IBS beams is 13.71 m 3 .

The difference in slab depth between the two systems is 12.5 cm; the concrete volume of the half precast slab is greater by 75m 3 per floor. Additional 225m 3 of concrete will be required if all slabs will be switched from conventional to IBS.

Results analysis (1)

The drawings show that there is no slab in the ground floor; Fs equals 1 when pre-cast columns and beams are used. The roof is to be casted by using TFS; F s =0. If a combination of TFS slab and pre-casted beam and columns for the roof and the first and second floors, the F s of table 1 will equal to 0.6. Hence the contribution of the structural part will be 28.2 to the IBS score. This contribution plus the 28% of the other two tables will yield 56.2%. This score satisfies the regulation of CIDB for private projects (not less than 55%). The cost of this satisfaction on the bases of concrete volume equals to (13.71 11.745) =2m 3 which is approximately 8% of the total volume of the concrete. The slab volumes remain at the lower value; 43m 3 per floor. The factor of wastes for in-situ casted concrete is estimated by 3% [6]. However, the same factor for precast concrete can be considered 0% due to possibility of recycling. Hence the actual difference can be forecasted by only 5%.

Results analysis (2)

Another scenario will be examined to satisfy the regulation regarding governmental buildings, the slabs are casted by using RFS and columns and beam are pre-cast.

The contribution of table 1 equals 50× (1/4+0.7×2/4)=30%.

The total IBS score is 58% which is less than CIDB requirements. That means at least one floor slab (including roof) must be precast concrete.

The contribution of the structural part for a case of (No floor, TFS, and precast roof slab) equal 40% which less than 42% required to satisfy CIDB requirements.

Using RFS for floor slabs will improve this value to be 42.5% and the total IBS score of 70.2% which is accepted by CIDB for government building projects. Any other scenario of improvement will propose using precast slab and this will increase the required volume of concrete.

Conclusion and recommendations

The current regulations will encourage private sector to use precast column and beams because a margin of 3% in concrete volume may be accepted as a cost for the higher quality and time saving.

Designer and contractor of government buildings have to expect that most of their future projects will include precast slab as well as precast columns and beams.

Using of Block work instead of brickwork will contribute by 10% to the IBS score.

It is recommended that more studies related to the use of some optimization techniques like the Artificial Intelligence Algorithms (AIA) will lead to better understanding for the impact of IBS score on the construction industry of Malaysia.