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Consulting Engineers Professional Engineers • Repair & Restoration • Project Management • Inspection Specialist Investigation • Civil & Structural Engineering • Environmental Management
194 Pandan Loop #07-19A Tel : (65) 6872 6679 Pantech Complex Fax : (65) 6873 0935 Singapore 128383 E-Mail : [email protected]
Harvest
STRUCTURAL INVESTIGATION AND SOIL INVESTIGATION OF BEACH ROAD / MIDDLE
ROAD BUILDING SITES
NOVEMBER 2006
NOTE
Legal & Intellectual Property of Harvest Consulting Engineers. All Rights Reserved. You are not allowed to duplicate, utilized the information based on the content herein to carry out any form of works without the written consent from either the client (URA) or Harvest Consulting Engineers.
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CONTENT S/No Description Page 1 Introduction 3 2 General information on the existing buildings 4 - 23 3 Determination of the structural supporting system for the buildings 24 - 26 4 On-site Testing and Scanning 27 - 28 5 Investigation, Analysis & Findings 29 - 57 6 Recommendations 58 - 64 7 Annex A – Photographic records of Block 1 8 Annex B – Photographic records of Block 9 / Main Building 9 Annex C – Photographic records of Block 14 10 Annex D – Photographic records of former NCO Club 11 Annex E – Calculations of loadings and determination of Allowable imposed loadings 12 Annex F – Carbonation Test Report 13 Annex G – Windsor Probe Test Report 14 Annex H – Plate Bearing Test report
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1. Introduction 1.1 Harvest Consulting Engineers was appointed by the Urban & Redevelopment
Authority to provide a professional structural investigation and soil investigation of Beach Road / Middle Road Building Sites. The investigation commenced on 4 October 2006. This report shall provide the records, analysis and findings of our investigations as well as on-site tests as carried out.
1.2 The building sites consist of 4 Buildings as follows :-
(a) Main Auditorium – Block 9 or Block B – along Beach Road (b) Block 1 or Block A – along Beach Road / Middle Road (c) Block 14 or Block C – along Beach Road (d) Former NCO Club – along Beach Road
LOCATION PLAN
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2. General Information on the existing buildings From our site investigation, we noted that the four buildings were built using conventional Reinforced Concrete Beam, Slab & Column configuration with the slab supported by the beams while the columns taking the floor loads into the foundation.
2.1 Block 1 / Block A
Block 1 is situated at the corner of the former Beach Road Camp fronting the beach road and the side along the Middle Road (See Location Plan) It is a two-storey reinforced concrete structure with conventional beam, slab and column configuration, with half of its span being reinforced concrete flat roof loft and the above with a Steel Truss-Timber Pitch Tiled-Roof Cover while the remaining half being directly covered by the pitch roof structure. (See Floor Layout Plan). There is no staircase access to the roof area except for ceiling openings (in the case of the R.C. Flat Roof Area) while at the remaining void area Typically, the span between reinforced concrete beam supporting the one-way spanning floor slab is estimated between 2.0m and 2.5m when viewed from 1st Storey. The general condition of the structure is satisfactory except for some minor spalling at the 2nd storey slab soffit just above the 1st storey toilet area.
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LAYOUT PLAN OF BLOCK 1 / BLOCK A (1ST & 2ND STOREY)
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LAYOUT PLAN BLOCK A (ROOF LEVEL BELOW ROOF COVER)
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View of Soffit of R.C. Roof Slab
View Roof Truss- Timber Pitch Roof below Roof
VOID
View of 2nd Storey Reinforced Concrete Beams and Slabs from 1st Storey
Front Elevation View of Block A Facing Beach Road
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Front Elevation View of Block A Facing Block 9
2.2 Block 9 & Main Building
Front Elevation of Block 9
Block 9 is situated at the rear of the site fronting Nicholl Highway. (See Location Plan)
Main Building is located from the main gate entrance facing Beach Road. Both block 9 and the main building are interconnected between level 1 and 2.
Block 9 is a 2-storey reinforced concrete structure with a reinforced concrete flat roof loft and a Steel Truss-Timber Pitch Tiled-Roof Cover. There were several openings for access to the roof loft area. There is no staircase access to the R.C. Flat roof loft area.
The main building is used as an auditorium at 2nd storey and it is a reinforced concrete structure with 2 levels (i.e. 1st Storey & 2nd Storey) with an internal upper 2nd storey at the side wings of the auditorium at 2nd storey.
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Front Elevation of Main Building (Beach Rd) Rear Elevation of Block 9
MAIN BUILDING PHOTOS
2nd Storey, Upper 2nd Storey and Roof Level View from Auditorium
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Side Elevation (East)from Block 9 Side Elevation (West) View from Front
Side Elevation (West) View From Back Side Elevation (East)
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LAYOUT PLAN OF BLOCK 9 & MAIN BUILDING
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The third storey of the main building consist of two side wings only (See Location Plan) and are accessible by the respective R.C. Staircases. At each wing of the 3rd storey area, there are 2 rooms and 1 staircase landing area. Above the 3rd storey area is a reinforced concrete flat roof. The end walls of the Main Building above 2nd storey is of Reinforced Concrete.
View of Main Staircase to 2nd Storey Auditorium Area
View of R.C. Flat Roof Above 3rd Storey Wing Sections
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View of R.C. Floor Slab – 2nd Storey Auditorium Area – Scanning in Progress
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2.3 Block 14 / Block C
Block 14 is situated at the front of the former Beach Road Camp along Beach Road next to the former NCO Club.
Front Elevation of Block 14 View from Beach Rd
Rear Elevation of Block 14 View from Nicholl Highway
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Side Elevation of Block 14 View from Main Building
The structural system of Block 14 is quite similar to Block 1 at 2nd Storey and as described under section 2.1. Block 14 is a two-storey reinforced concrete structure with conventional beam, slab and column configuration. It appeared from external views that the existing pitch roof is of a Steel Truss-Timber Pitch Tiled-Roof Cover. Typically, the span between reinforced concrete beam supporting the one-way spanning floor slab is estimated between 2.0m and 2.5m when viewed from 1st storey.
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2.4 Former NCO Club
The former NCO Club is situated along the corner of Beach Road next to the former Beach Road Camp.
Front Elevation of NCO Club from Beach Rd
Side Elevation of NCO Club
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Rear Elevation of NCO Club
Rear Balcony Area of NCO Club
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The structural system of the former NCO Club is of the conventional reinforced concrete slab, beam and column configuration. We were unable to gain access (Chained Locked) to part sections of level 2 & 3 of the building during the time of our investigations from 1st storey to Roof as covered in this preliminary report. NCO Club is a three-storey reinforced concrete structure with conventional beam, slab and column configuration. The pitched roof covering consisted of Sloping RC Beam supporting timber purlins and battens so as to hang the clay tiles as installed.(See Annex D, photo no 25)
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LAYOUT PLAN OF BLOCK 14 (Block C)
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Former NCO Club – Ground Floor & Mezzanine Floor Layout Plan
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Former NCO Club – Basement Layout Plan
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Former NCO Club – First Floor Layout Plan
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Former NCO Club – Second Floor Layout Plan
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3. Determination of Structural Supporting System for the buildings
As we do not have any records of existing as-built structural plans, the first
phase of the structural investigation is to determine the design of the (4) four buildings whether they were built using load-bearing wall system or reinforced concrete system. From our visual survey, we noted that the structural system of the four (4) buildings was of conventional reinforced concrete slab, beam and column configurations.
In order to ascertain the said, we adopted a proprietary scanning system (using HILTI Model Ferroscan PS200, See Photo below)
Photo 3a-Scanning of R.C. Floor Slab In Progress
Photo 3b-The Analysed Picture of the Installed Reinforcement within the floor slab
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Photo 3c-The Analysed Picture of the Installed Reinforcement within a R.C. Beam
Photo 3d-The Analysed Picture of the Installed Reinforcement within a R.C. Column
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The scanning was carried out on all (4) four buildings systematically. Some photo evidences of the scanning works can be shown in the photos below. This is a non-destructive method to reveal the reinforcement layout and at the same time to provide an approximate dimensions for the cover to the concrete, spacing layout of the reinforcement as well as the diameter of the reinforcement steel. With the diameter of the steel reinforcement established from scanning, we can also co-relate with those reinforcement from spalled concrete area to determine the degree of deterioration of the corroded ones. This is further justified through the carbonation tests There were no evidences of any load bearing mansonry walls on the four buildings during the time of our investigation. All four buildings as scanned confirmed that their design as-built were actually reinforced concrete based structural system.
Scanning In Progress – NCO Club
Scanning In Progress – Main Auditorium
Photo 3d
Photo 3e
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4. On Site Testing & Scanning The following soil investigation and on-site tests were conducted before 3
November 2006 :
(a) Soil Investigation Works for 2 boreholes (Report as submitted)
(b) Foundation Bearing Capacity – Plate Bearing Test
(c) Determination of Existing Concrete Strength using Windsor Probe Tests (Non-destructive Method)
(d) Carbonation Tests on spalled concrete area to determine the degree of
corrosion of the embedded reinforcement bar.
(e) Scanning of Reinforcement Steel to establish the layout of the reinforcement using HILTI Ferroscan PS200.
Photo 4a – Showing our specialist using the Scanning Equipment
(f) Tilt measurement of structure (externally) using a bubble leveling
scope (g) Probing of Walls / Columns using a 3mm Borescope.
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Photo 4b – Showing our technical specialist using a borescope to view the condition of
existing reinforcement within the concrete – In this case a R.C. Wall
(h) Moisture Measurements to determine the moisture content within the concrete section.
Soil Investigation Works – Borehole 1
Near Block 9
Soil Investigation Works – Borehole 2 Near Block 14
Plate Bearing Foundation Test – Next to Borehole 1
Plate Bearing Foundation Test
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5. Investigation, Analysis & Findings
All four (4) buildings were investigated systematically by first carrying out a tilt measurement externally, survey of any external defects from ground to roof level followed by internal surveys. After which a detailed scanning on selected locations internally on structural elements using our scanning tool so as to be able to determine the defective areas which shall require attention. We have classified the defects classifications into 3 categories as follows :- Type 1 : Internal & External structural supporting elements with very
severe defects. Building tilting or differential settlement causing serious defects to columns in the main structure where reconstruction is required.
Type 2 : Internal & External structural supporting elements with moderate
defects. Building tilting slightly or minor settlement causing moderate defects to columns in the main structure where only localized reconstruction is required.
Type 3 : Internal & External structural supporting elements with very mild
or minor defects. Building does not have any signs of significant tilting whereby general repairs to the structure is only required.
5.1 Block 1 / Block A From our internal, external survey and investigation except for some areas
within 1st storey as it is inaccessible during the time of our investigation. Generally, the building is in satisfactory condition with only localized defects. This building can be classified under Type 3.
The defects as detected during our time of investigation :-
(a) Exterior Generally, the roof tiles appeared to be porous during the time of our investigation causing water seepages and thus wood decays on timber sections.
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Photo 5a - Traces of external sunlight entering from the roof tiles can be seen internally when
view at 2nd storey (b) Interior
There was a localized concrete spalling on location B1-1 at the roof R.C. beam when view at 2nd Storey. (See Defect Plan No. 5.1)
Photo 5b – A localized R.C. beam concrete spalling due to corroded reinforcement
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Location B1-1 Spalled Concrete Beam
Defect Plan No. 5.1
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A carbonation test (See Photo 5c) and corresponding scanning of the affected beam on the spalled area and the unaffected length revealed that the entire length of the steel reinforcement had been mildly corroded of which the oxidation process had caused the spalling to take place.
Photo 5c – Photo Evidence of Carbonation Test being carried out to determine the length of
the corrosion of the particular reinforcement
The carbonation depth as reflected in the test results from the accredited laboratory indicated an average of 97mm. A half cell test shall then be carried out to determine the depth of corrosion which shall be included in the final report. From our scanning of the beam, it indicated that 80% of the length of the reinforcement is affected by the corrosion process.
Generally at the roof beam and slab locations, the moisture readings ranges from 30% to 65% which indicated severe water seepages from above the roof.
Photographic records of the findings of this building for 2nd storey can be found in Annex A of this report.
The following photos from 5c(1) to 5c(9) were the photographic evidences of the current conditions of the soffit of 2nd storey beams, slabs and columns during the time of our investigation. The only minor defects spotted as indicated in photo 5c(6) was a localized spalled concete slab section and in photos 5c(7) to 5c(9) showing the water dampness of the ceiling slab within the guard house. The roof shall require water-proofing treatment.
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Photo 5c(1) – Photo of 1st Storey Corridor – Facing Guard House
Photo 5c(2) – Photo of 1st Storey Office Room 1
Photo 5c(3) – Photo of 1st Storey Office Room 2 –Paint Peeling
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Photo 5c(4) – Photo of 1st Storey Corridor – Facing Middle Road
Photo 5c(5) – Photo of 1st Electrical Storey Switch Room
Photo 5c(6) – Photo of 2nd Storey Soffit Ceiling Slab @ 1st Storey Toilet
(Side of Building facing Middle Road)
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Photo 5c(7) – Photo of Guard House of Block 1
Photo 5c(8) – Photo of Roof Slab - Guard House of Block 1 (Water Seepage)
Photo 5c(9) – Photo of Roof Slab - Guard House of Block 1 (Water Seepage)
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5.2 Block 9 / Main Building Block 5.2.1 Block 9
From our internal and external survey and investigation, generally, the building is in satisfactory condition with only localized defects. This building can be classified under Type 3.
The defects as detected during our time of investigation are as follows :- (a) Exterior
Generally, the roof tiles appeared to be porous during the time of our investigation causing water seepages. The R.C. Flat Roof Awning at the Rear Section (See Photo 5d below) had evidences of water seepages with high water moisture content of close to 45% during the time of our investigation.
There was a localized concrete spalling along the soffit of the RC Awning slab (See Defects Location B2-1 of Defect Plan No. 5.2)
Photo 5d(1) - Localised Spalling & Dense Water Seepages
Photo 5d(2) – Close Up View
Photographic records of the findings of this building can be found in Annex B of this report.
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5.2.2 Main Building
From our internal and external survey and investigation, generally, the building is in satisfactory condition with only localized defects externally which can be classified under Type3. However, internally at the 2nd Upper Storey locations, there were considerable amount of defects of which this shall be classified under Type 2.
The defects as detected during our time of investigation are as follows :- (a) Exterior
Generally, the roof tiles appeared to be porous during the time of our investigation causing water seepages to the sloping roof and all terraced RC slabs internally above 2nd Upper Storey. The R.C. Fins externally (At Upper 2nd Storey Level) were found to be weak in the connections to the attached structure during our physical examination (See Photo 5e below) and at some locations were cracked and hanging precariously.
Photo 5e – View of External RC Fins along the Main Building
The extent of the defects were indicated in defect Location B2-2 of the Defect Plan No. 5.2
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Location B2-1Spalled Concrete Slab
(Soffit)
Defect Plan No. 5.2
Location B2-2Spalled R.C. Fin
(Exterior)
Location B2-2Spalled R.C. Fin
(Exterior)
Location B2-4 Spalled R.C. Beam, Slab
& Wall (Interior)
Location B2-5 Spalled R.C. Beam & Slab
(Interior)
Location B2-7Wetted R.C. Slab & Beam (Interior)
Location B2-6 Wetted R.C. Slab
(Interior)
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Location B2-8Localised Roof Collapse
(Exterior)
Defect Plan No. 5.3
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There is a localized roof collapse (See Defect Location B2-8 of Defect Plan No. 5.3) during the time of our investigation. The collapse appeared to be due to weak roof sections and weathering due to inadequate roof waterproofing causing the localised collapse. (See Photo 5f below)
Photo 5f – View of External Roof Defects Photo 5f – View of Roof Defects Internally (b) Interior
Most of the obvious defects were at 2nd upper storey and above where there were clear evidence of high amount of water seepage from external roof. As a result of the defects, we have classified 2 locations under type 2. These locations can be found in the defect plan no. 5.2 under defect locations B2-4 and B2-5. At location B2-4, there were concrete spalling to R.C. beam, slab and wall. (See photo 5g below)
Photo 5g View of Dislodged Corroded Steel
Reinforcement from RC Beam (B2-4)
View of Dislodged Corroded Steel Reinforcement from RC Beam (B2-5)
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A carbonation test (See Photo 5h) and corresponding scanning of the affected beam on the spalled area and the unaffected length revealed that the entire length of the steel reinforcement had been mildly corroded of which the oxidation process had caused the spalling to take place.
Photo 5h(i) – Photo Evidence of Carbonation Test being carried out to determine the length
of the corrosion of the particular reinforcement (Location B2-4)
The carbonation depth as reflected in the test results from the accredited laboratory indicated an average of 78mm for Beam and 27mm for the slab respectively (See Annex F for test report). A half cell test shall then be carried out to determine the depth of corrosion which shall be included in the final report. From our scanning of the beam and slab, it indicated that 90% of the length of the reinforcement is affected by the corrosion process.
Generally at the roof beam and slab locations, the moisture readings ranges from 50% to 75% which indicated severe water seepages from above the roof slab requiring attention.
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Photo 5h(ii) – Photo Evidence of Carbonation Test being carried out to determine the length
of the corrosion of the particular reinforcement (Location B2-5) The carbonation depth as reflected in the test results from the accredited laboratory indicated an average of 97mm for the beam and 48mm for the slab respectively (See Annex F for test report). A half cell test shall then be carried out to determine the depth of corrosion which shall be included in the final report. From our scanning of the beam and slab, it indicated that 92% of the length of the reinforcement is affected by the corrosion process.
Generally at the roof beam and slab locations, the moisture readings ranges from 50% to 85% which indicated severe water seepages from above the roof slab requiring attention. Photographic records of the findings of this part of the building for 2nd Upper Storey (3rd Storey) can be found in Annex B of this report.
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At location B2-6, there were minor concrete spalling to R.C.slab of crack width of 1mm. (See photo 5i below). However, the concrete surfaces is very damp with moisture readings of 55% to 78% during the time of our investigation.
Photo 5i View of Wetted Slab & Beams Due to Extreme Water Seepage (B2-6)
At location B2-7, there were minor concrete spalling to R.C.slab and beams as well as cracklines with crack width ranging from 2.5mm to 3mm. (See photo 5j below). However, the concrete surfaces is very damp with moisture readings of 65% to 80% during the time of our investigation.
Photo 5i View of Wetted Slab & Beams Due to
Extreme Water Seepage (B2-7) Photo 5i View of Wetted Walls Due to Extreme Water Seepage (B2-7)
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Due to the quantum of defects above 2nd Upper Storey (3rd Storey) and above, a steel staging had been erected at the corner wall near location B2-5 (See photo 3j below)
Photo 5j View of specially designed Steel Staging for the testing and scanning of the current condition
of the RC Curved Spine Beam, Ceiling Slab, Beams and Columns
In order to ascertain the existing concrete compressive strength under damped condition, we had carried out a non-destructive Windsor-Probe test at this location (see photo 3k below) of the arched R.C. column. From the accredited laboratory test results (see Annex G), the tested concrete cube compressive strength is 29.6N/mm2 . We shall assume that this will be the critical compressive concrete strength for the main building. As such, we shall also adopt fcu (concrete), of characteristic strength of 20N/mm2 instead (as this will be more representative instead of 29.6N/mm2). In order to determine the allowable imposed loading of the main building (of which the beam/slab configuration is similar to the remaining 3 buildings), we carried out a back-analysis by taking into account of the beam/slab reinforcement layout, sections, reinforcement as installed, and the concrete strength as above. Details of the said analysis and calculations can be found in section 5.5 and Annex E of this report.
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Photo 5k- Photo of Windsor Probe Test to determine the concrete
compressive strength on a RC Arch Column near location B2-5
More photo evidence of Defects along Main Block on Spalled and Damaged R.C. Fins Photo Nos 5k(1) to (6)
Photo 5k(1) – View of R.C. Fins
Photo 5k(2) –Spalled R.C. Fins
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Photo 5k(3) – Another Cracked R.C. Fins Photo 5k(4) – Another Cracked R.C. Fins
Photo 5k(5) – Another Cracked R.C. Fins
Photo 5k(6) – Another Cracked R.C. Fins
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Photos of 2nd Upper Storey Rooms & Corridor (Near the Main Gate) – Main Block (Photo Nos 5k(8) to 5k(12)) – DEFECTS ONLY
Photo 5k(7) – Cracklines above roof slab between Blk 9 and Main Block
Photo 5k(8) – Localised Spalling of Concrete Slab (Soffit) 2nd Upper Storey - Main Block
Photo 5k(9) – Localised Concrete Spalling along RC Beam 2nd Upper Storey Main Block
Photo 5k(10) – Severe Dampness along soffit of
RC Beams and Slab Room 3
Photo 5k(11) – Localised Concrete Spalling Photo 5k(12) – Severe Dampness
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5.3 Block 14 From our internal, external survey and investigation, generally, the building is in satisfactory condition with only localized defects internally and externally which can be classified under Type 3.
The defects as detected during our time of investigation are as follows :- (a) Exterior
Generally, the roof tiles appeared to be porous during the time of our investigation causing some minor water seepages to the 2nd storey area. There were only evidences of minor ground settlement along location B2-10 on defect plan no. 5.4 (see photo 3L below). It was noted during the time of investigation that there was an underground (Circle Line) project adjacent to the subject building and this could have possibly cause the settlement along the external apron slab since the underlying subgrade consisted a thick layer of soft compressive marine clay. There were no visible signs of R.C. columns tilting as measured on site nor structural cracks, spalling or visible distress to all supporting elements during the time of our investigation.
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Location B2-10Concrete beam Spalling
(Interior)
Location B2-9Minor Ground
Settlement (Exterior)
Defect Plan No. 5.4
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Photo 5L(a)- View of typical ground settlement along non-suspended apron slab along location B2-9
Photo 5L(b)- View of typical ground settlement along non-suspended apron slab along location B2-9
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(b) Interior
There is only a localized R.C. beam spalling due to water ingress possibly from leaks of a nearby a sewer pipe (See photo 5m below and also the defect location B2-10 of Defect Plan No. 5.4) . From the scanning along the span of the affected beam, it appeared that ½ the span of the beam had been affected by the corrosion.
Photo 5m- View of localized concrete spalling along location B2-10
Photo 5n- View of Water Seepages from the R.C. Flat Roof Slab
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5.4 Former NCO Club
From our internal, external survey and investigation, generally, the building is in satisfactory condition with only minor defects internally which can be classified under Type 3.
The defect as detected during our time of investigation was isolated mainly within the 2nd Basement Plant Room area along location B2-11 on defect plan no. 5.5 (see Photo 5p & 5q below). As shown, the entire soffit of the slab were damped with water/high moisture.
The moisture measurements as taken on site were between 65% and 80% which is highly damped indicating a severe ingress of water externally.
Photo 5p- View of Water Seepages on the soffit R.C. Slab – Plant Room
Photo 5q- View of Water Seepages from Basement Wall / Slab
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Location B2-11 Severe Dampness to
Soffit of Concrete Slab (Interior)
Defect Plan No. 5.5
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5.5 DETERMINATION OF ALLOWABLE IMPOSED LOADING & ANALYSIS
As described earlier in section 5.2 of this report, we have conducted a series of non-destructive Windsor Probe Tests on Block 1, Main Building as well as the former NCO Club so as to obtain the as-built compressive concrete strength. The results of the test report from the accredited laboratory can be found in Annex G. The results of the compressive concrete cube strength are as follows :- (a) Block 1 - 45.2 N/mm2 (b) Main Building - 29.6 N/mm2
(c) NCO Club - 46.3 N/mm2
For a concise concrete strength, we have taken the critical strength of 29.6 N/mm2 instead of just of taking a mean value and adopted a concrete characteristic strength of 20.0 N/mm2 in our back analysis for being conservative. As described earlier in our report under section 3 of determining the structural system using HILTI PS200 Ferroscan, we were able to determine an estimated size of the reinforcement steel as well as the spacing, cover of the reinforcement steel embedded within the concrete section. From site measurements of critical beam and slab arrangements, we noted that the critical span is located in the main building auditorium (2nd Storey) . The sizes of the slabs, beams and columns were determined and this was followed by a back analysis by using the basic reinforced concrete analysis under CP110 of the former code of practice instead of current local code of practice SS/CP65 or British BS 8110. The steel reinforcement diameter was determined from the scan and we assumed that the steel reinforcement is of MILD steel instead of High-Yield ones as used currently in the industry. As calculated and demonstrated in our calculations in Annex E of this report, the typical one-way spanning slab is capable of handling 4.0 KN/m2 of imposed loadings for commercial use (as it passed the design requirements) for all four (4) buildings on 2nd storey and above. The typical span between the supporting beams was about 2.0m
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5.6 DETERMINATION OF FOUNDATION BEARING CAPACITY
In order to correlate the loading from roof level right down to the foundation, a plate bearing test was conducted by assuming an allowable bearing capacity of 150 KN/m2 before the commencement of the test.
As joint inspected with the S.O. of our client, it was agreed that we assumed the loading from the heaviest structure (i.e. Main Building) and to simulate the loading into the foundation. As such, we decided to carry out the foundation capacity test by means of the plate bearing test (by M/s ABV) The test can only be commenced on 3 November 2006 and as such, the report is not ready during the time of the preparation of this interim report. However, we were able to obtain the loading graph showing the Loading and Settlement Values (See Annex H) As the plate size for the test is relatively small of 300mm dia., we shall have to adopt a factor of 3.0 and assuming an absolute max settlement of 30mm as the limit Force/Stress on the applied location at 1.5m below the ground level.
Photo 5s- View of location of Trial Pit (Near Block 9)
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View of Plate being loaded upto 420KPa where corresponding strains were measured
Bearing Plate Diameter = 300 mm
Bearing Pressure Settlement (kPa) (mm)
0 0.00 50 0.48
100 2.32 150 4.19 200 6.63 250 9.93 300 14.11 350 19.51 400 26.96 450 34.59 300 33.51 150 32.85
0 26.10
Bearing Pressure @ Failure = 420 kPa
Plate Bearing Test – Bearing Pressure Vs Settlement
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From the results of the graph, it was noted that the failure bearing pressure is about 420 KN/m2. As such, the allowable soil bearing capacity should be in the region of 420.0 / 3.0 = 140.0 KN/m2. This is quite close to our assumed bearing capacity. As demonstrated by calculations in Annex E of this report, the design foundation acting soil pressure is about 124KN/m2 with an imposed loading of 4.0 KN/m2 which is within the allowable soil bearing capacity of 140.0 KN/m2(*). However, it was noted that the assumed footing foundation size in the calculations of only 2m width strip footing at each column location was conservative. As such, we must assume that the maximum loadings allowable as demonstrated in the calculations were verified as its maximum and the building foundation CANNOT handle any further additional loadings on the structure as a result of Additions / Alterations works. This should be verified again by a professional engineer through appropriate analysis and calculations instead of taking the values as given in this report. As there were no visible or significant settlement during the time of our investigation for all (4) four buildings, and that these buildings had been utilized for assembly (Military Usage) purposes for a long period of time, the maximum allowable bearing pressure of 140 KN/m2(*) as tested shall be acceptable taking into consideration of the current soil condition as investigated from the two boreholes in the soil investigation report. (*) This is only a single test approximation at one location to deduce the existing foundation capacity. The Professional Engineer shall have to exercise and to carry out his professional assessment by having more foundation tests at random / other locations in order for a accurate determination of the required capacity.
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6. RECOMMENDATIONS 6.1 Defects Rectification
In this report, the defects as described under section 5 from the findings clearly indicated that the root cause of the defects were mainly due to water-seepages, and the secondary cause could be due to weathering and poor maintenance. Most of the roof tiles except for the NCO Club, that is, Block 1, Block 9, Main Building and Block 14 were in poor conditions that shall require attention. The following shall provide some prominent repair requirements whereas further detailed repair requirements shall be covered under the final report. The recommendations were made based on the findings during the time of investigation. Any defects as discovered beyond our investigation period will not be reflected herewith.
Block 1 Repair requirements:-
(a) Replacement of existing old defective roof tiles (b) Thorough Inspection of Timber Purlins & Battens by engaging a pest
control specialist to reveal for any termite borings which may weaken the timber section.
(c) Anti-Rust treatment to all roof steel-trussed structural frame followed by a finishing coat of epoxy-based coating.
(d) To carry out general repairs to the entire R.C. Flat roof areas. (e) General Water-proofing treatment to entire R.C. Flat Roof Area (Also
above the Guard House Structure) (f) Repair the entire length of the spalled reinforced concrete beam
(Defect Location B1-1) – The corroded steel reinforcement shall be replaced with new ones and lapped with existing ones either by lapping along the existing good ones of the adjacent connecting bars. The concrete sections along the hacked area shall be exposed and to be monitored by a professional moisture meter to ascertain whether the moisture content is dry enough to grout back by means of epoxy-resin mixed with cement mortar and final rendering to finished section as per original beam section.
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Block 9 Repair requirements:-
(a) Replacement of existing old defective roof tiles (b) Thorough Inspection of Timber Purlins & Battens by engaging a pest
control specialist to reveal for any termite borings which may weaken the timber section.
(c) Anti-Rust treatment to all roof steel-trussed structural frame followed by a finishing coat of epoxy-based coating.
(d) To carry out general repairs to the entire R.C. Flat roof areas. (e) General Water-proofing treatment to entire R.C. Flat Roof Area (f) Repair the entire panel of the spalled reinforced concrete slab (Defect
Location B2-1 - See Diagram below ) – The corroded steel reinforcement shall be replaced with new ones and lapped with existing ones either by lapping along the existing good ones of the adjacent connecting bars. The concrete sections along the hacked area shall be exposed and to be monitored by a professional moisture meter to ascertain whether the moisture content is dry enough to grout back by means of epoxy-resin mixed with cement mortar and final rendering to finished section as per original beam section.
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Main Building - Auditorium Repair requirements:-
(a) Replacement of existing old defective roof tiles (b) Thorough Inspection of Timber Purlins & Battens by engaging a pest
control specialist to reveal for any termite borings which may weaken the timber section.
(c) Anti-Rust treatment to all roof steel-trussed structural frame followed
by a finishing coat of epoxy-based coating.
(d) To carry out general repairs to the entire R.C. Flat roof areas.
(e) General Water-proofing treatment to entire R.C. Flat Roof Area.
(f) Fibre-Resin Enhancement to all 2nd Storey RC Beams to Specialist Requirements.
(g) Repair the entire length of the spalled reinforced concrete beam
(Defect Location B2-4 to 7) – The corroded steel reinforcement shall be replaced with new ones and lapped with existing ones either by lapping along the existing good ones of the adjacent connecting bars. The concrete sections along the hacked area shall be exposed and to be monitored by a professional moisture meter to ascertain whether the moisture content is dry enough to grout back by means of epoxy-resin mixed with cement mortar and final rendering to finished section as per original beam section.
(h) Repair the entire panel of the spalled reinforced concrete slab (Defect
Location B2-7 - See Diagram below ) – The corroded steel reinforcement shall be replaced with new ones and lapped with existing ones either by lapping along the existing good ones of the adjacent connecting bars. The concrete sections along the hacked area shall be exposed and to be monitored by a professional moisture meter to ascertain whether the moisture content is dry enough to grout back by means of epoxy-resin mixed with cement mortar and final rendering to finished section as per original beam section.
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(i) R.C. Fins - Repair by hacking existing fins to review for corrosions
within and to adjacent connecting elements in order to exposed the reinforcement along Defect Location B2-2) – The corroded steel reinforcement shall be replaced with new ones and lapped with existing ones either by lapping along the existing good ones of the adjacent connecting bars. The concrete sections along the hacked area shall be exposed and to be monitored by a professional moisture meter to ascertain whether the moisture content is dry enough to grout back by means of epoxy-resin mixed with cement mortar and final rendering to finished section as per original beam section.
(j) To rebuild the collapsed roof structure to existing condition at defect
location B2-8
We recommend a localized re-construction using original design for defect location B2-4 to 6 of the upper 2nd Storey Level / (3rd Storey)
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Block 14 Repair requirements:-
(a) Replacement of existing old defective roof tiles (b) Thorough Inspection of Timber Purlins & Battens by engaging a pest
control specialist to reveal for any termite borings which may weaken the timber section.
(c) Anti-Rust treatment to all roof steel-trussed structural frame followed by a finishing coat of epoxy-based coating.
(d) To carry out general repairs to the entire R.C. Flat roof areas. (e) General Water-proofing treatment to entire R.C. Flat Roof Area. (f) Repair the entire length of the spalled reinforced concrete beam
(Defect Location B2-9) – The corroded steel reinforcement shall be replaced with new ones and lapped with existing ones either by lapping along the existing good ones of the adjacent connecting bars. The concrete sections along the hacked area shall be exposed and to be monitored by a professional moisture meter to ascertain whether the moisture content is dry enough to grout back by means of epoxy-resin mixed with cement mortar and final rendering to finished section as per original beam section.
(g) At Defect location B2-10, the settled/void area of the non-suspended apron slab should be hacked and exposed the subgrade below. The ground should be filled with aggregates and sand and compacted and re-cast to original apron details to correct finishing level.
(h) Repair the entire panel of the spalled reinforced concrete slab (Defect Location B2-1 - See Diagram below ) – The corroded steel reinforcement shall be replaced with new ones and lapped with existing ones either by lapping along the existing good ones of the adjacent connecting bars. The concrete sections along the hacked area shall be exposed and to be monitored by a professional moisture meter to ascertain whether the moisture content is dry enough to grout back by means of epoxy-resin mixed with cement mortar and final rendering to finished section as per original beam section.
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Former NCO Club Repair requirements:-
(a) To inspect existing clay roof tiles to ascertain the conditions on whether to be replaced on the defective ones.
(b) Thorough Inspection of Timber Purlins & Battens by engaging a pest control specialist to reveal for any termite borings which may weaken the timber section.
(c) To carry out general repairs to the entire R.C. Flat roof areas. (d) General Water-proofing treatment to entire R.C. Flat Roof Area. (e) Specialist Water proofing treatment by injection grouting to Basement
Walls and Slabs in defect location B2-11 (plant Room Area) (f) Fibre-Resin Coating Repair to Specialist Requirements. (g) Fibre-Resin Coating Enhancement to all 1st, 2nd and 3rd Storey R.C.
Beams & Columns. (h) Repair the entire panel of the spalled reinforced concrete slab (Defect
Location B2-11 - See Diagram below ) – The corroded steel reinforcement shall be replaced with new ones and lapped with existing ones either by lapping along the existing good ones of the adjacent connecting bars. The concrete sections along the hacked area shall be exposed and to be monitored by a professional moisture meter to ascertain whether the moisture content is dry enough to grout back by means of epoxy-resin mixed with cement mortar and final rendering to finished section as per original beam section.
6.2 Temporary Protection 6.2.1 Under Type 2 of the classification for Main Building, we recommend that the
defective beams at locations B2-4 and B2-5 be propped immediately at the center of the beam and slab using a 2-Tonne Steel Props available in the market. This is to prevent any sudden collapse due to extreme dampness and deterioration of steel and concrete integrity. (The area required for the said protection is only isolated to 2nd Upper Storey of the Main Block Area – Both Wings)
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6.2.2 At the rear of the cantilever roof slab awning of Block 9, of which a large area
of concrete spalling occurred (See Photo 5d(1) and 5d(2)). The entire length of the cantilever slab shall require some temporary steel staging support until roof repairs and water proofing works were completed.
6.3 Owing to the age of the building, there shall not be any further additions /
alterations to all (4) four buildings without a thorough and accurate assessment of the loading paths and ascertaining the load carrying capacity of the designed R.C. slabs, beams and columns as well as the maximum allowable foundation capacity.
6.4 The max allowable imposed loadings on the buildings shall not exceed 4.0 KN/m2. Also, please note that there shall not be any installation of heavy office equipment (e.g. Compactors, Tall Steel Cabinets) without the review and certification of a professional engineer. The client is advised to note that the original design the in 1930s did not take into account of such heavy equipments and as such, all office equipments shall be reviewed in detailed before installing into the buildings.
6.5 Any further increase in loadings and changes in loading paths shall require
foundation underpinning works and this must be designed by an experienced professional engineer with experience in repair and restoration works.
6.6 The description of the necessary repair and restoration works were given in
item 6.1. The main bulk of the rectification works will be at the main block (Auditorium) area, especially from 2nd Storey and above to roof level. All remaining three buildings shall have to undergo localized concrete repairs with re-roofing and water-proofing works. From experience on proper repair works, we have estimated about S$1.5Million for the Main block and Block 9 while Block 1 & 14 is about $0.8Million each. We have also estimated about $0.9Million for the repair and restoration of NCO Club. A preliminary estimation of $4.0Million is required for the entire repair and restoration works.
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