GAUTENG DEPARTMENT OF INFRUSTRUCTURE DEVELOPMENT

Transcription

1 GAUTENG DEPARTMENT OF INFRUSTRUCTURE DEVELOPMENT BUILDING ASSESSMENT REPORT STRUCTURAL FOR CORNER HOUSE AUG 2014 i P a g e

2 Table of Contents 1. INTRODUCTION Design Criteria and Specifications Scope of the Services Scheme Report STRUCTURAL ASSESSMENT Building configuration and interfaces with adjacent buildings Façade Roof Waterproofing and Roof Structures General Structural Floor Assessment Structural Column Assessment Foundations Basement and Basement Retaining Walls Building Internal Brickwork Building Internal Finishes and Services Staircases Structural Floor Loading Allowances Allowed For Future Use PHOTOGRAPHIC EVIDENCE AND COMMENT:... 7 ii P a g e

3 1. INTRODUCTION The project brief, as issued by Gauteng Funding Agency (GFA), was to conduct an initial assessment of the building condition, services, structural integrity of Corner House, and to provide recommendations regarding the repairs and renovations of the buildings. Corner House is an occupied building undergoing a ground floor refurbishment which involves renewal of services and renewing of interiors. This report deals with the structure as a whole and reports on the current state of the building on date of inspection excluding the ground floor area. Certain of the items listed in this report may be in the process of rectification with the current ground floor upgrade. The condition of the structural components is described below. 1.1 Design Criteria and Specifications This project will be implemented in compliance with all the requirements of the National Building Regulations and the new SANS10400, including any town planning prescripts of the local authority. 1.2 Scope of the Services Scheme Report This report deals with the proposed structural services to be implemented and preliminary design for the feasibility for the repairs and renovations of the existing building. 2. STRUCTURAL ASSESSMENT 2.1 Building configuration and interfaces with adjacent buildings. Corner House comprises 16 suspended office floors above ground, and 2 levels of roof slabs consisting of level 17 roof and localised level 18 roof (above the building core), and 3 basements below ground level. Hence the building consists of 17 floors and 3 basement levels. The building has no links to adjacent buildings. The building has a unique basement atrium currently used as a spill out space from lecture venues and entertainment area covered with a polycarbonate skylight. 2.2 Façade. The three street facades (North, East and South) consist of curtain wall which runs past all floor slabs from roof parapet level to the underside of second floor slab, on all facades. The Façade itself is in general in good functional condition, albeit faded and in need of visual improvement from an architectural perspective. The façade has been locally damaged from local rerouting of rainwater downpipes. The routing of these pipes is ad-hoc and is aesthetically displeasing. The water tightness of these diverted pipes and all other downpipes need to be checked as water entry into the building is noted in multiple locations. The façade from ground to first floor is a cementious render and strip window combination and is in good condition. A deep clean of this façade element is recommended. 3

4 The building has two internal ducts systems which are open to the atmosphere above. The internal ducts are in need of repainting and waterproofing improvements, most notably at the base of the ducts as it is evident that the ducts themselves are the cause of major water entry into the basement occupancies below. No window cleaning or fall arrest systems exist for cleaning the exterior face of the building. It is recommended that such a system is installed to ensure future aesthetic appeal of the building. 2.3 Roof Waterproofing and Roof Structures The 17 th floor roof slab and localised 18 th floor roof slab have recently had the torch on waterproofing replaced and is in excellent condition. Solar panels are being installed on these roofs, which has compromised the waterproofing as the contractor is drilling through the waterproofing to install anchors. It is also noted that all mechanical plant or any other installations such as solar panels with concrete plinths must have rubber bearing pads between the concrete pad or machine foot and the waterproofing, to prevent damage to the waterproofing system. The two central duct shafts and the one external duct shaft system are presently the source of major water entry issues in the basement occupancies below. It is recommended that the ducts are completely repainted vertically and horizontal penetration sealed in the walls themselves. The ground floor duct floor requires complete re-waterproofing and the renewal of the storm water drainage systems from these areas. It is further recommended that the entire duct is covered with a new soft roof system on structural steel substructure (raised and louvred vertically) to ensure no storm water enters the duct shafts and provides a waterproof cover for the duct shafts. Allow 40kg/m2 for the steel substructure and allow for rainwater goods to direct the soft roof water onto the level 17 roof slab below. It is noted that the executive penthouses on level 16 have localised external balconies on the north and south facades. The balconies appear to have had the waterproofing renewed with the roof slabs, however as access was not provided, this could not be confirmed. All of the building rainwater downpipes should be checked for leaks. Allowance should be made for renewing the rainwater downpipes throughout the building. On second floor it is noted that a large number of rainwater pipes have been rerouted in surface mounted pipes which have been installed in an ad-hoc manner around the building. These pipes need to re-routed in a consistent manner, and their presence included in a new architectural aesthetic elevation for each building face. The skylight on ground floor level on northern side of building (covering the basement entertainment area) requires complete panel replacement from both a functional and aesthetic perspective. At present this skylight and its associated internal gutter system is leaking directly into the entertainment areas below and adding to the water entry problem into the building s basements. A structural steel hoisting gantry is present on the roof slab above the eastern internal duct shaft. This hoist structure will need to be de-rusted and repainted, and the bolted connections checked for integrity before being re-commissioned with new regulatory signage showing the maximum lifting weight as 1 tonne. 4

5 2.4 General Structural Floor Assessment. The floors are constructed in one way spanning ribbed slabs, which load wide primary support beams which span between the building columns. The slab systems within the office building (that is ground floor upwards) are in good condition. The basement level slabs and the soffit of the ground floor slab show significant damage from ongoing water egress into the structure. The soffit reinforcement in 15% of the basement and ground floor slabs is rusting, and this results in spalling of the concrete cover. The waterproofing of the ground floor slabs under the external works, renewing of the downpipes and waterproofing of the internal and external duct systems is required prior to commencement of remedial works to correct the spalled concrete to the ground and basement slabs. The rusted reinforcement will need to be treated for rust and thereafter treated with a suitable structural epoxy protection, and the concrete cover reinstated with a structural patch plaster which is has to be secured to the soffit with a mesh suspended with chemical anchors to detail. 2.5 Structural Column Assessment. The building s concrete columns and concrete walls are in good condition. The perimeter columns of the building will need to be checked for structural integrity due to the issue regarding renewal of rainwater downpipes. The existing downpipes in a degraded state will reduce the capacity of the columns. It is recommended that new downpipes are installed outside the columns, and the old pipes within the columns filled with a 50MPa non-shrink grout, following a thorough system clean. 2.6 Foundations. There are no signs of visible foundation settlement of the building; hence the current building foundations are in good condition. 2.7 Basement and Basement Retaining Walls. The building has 3 basement levels comprising parking, safe areas, plant areas, storage areas, lecture venues and entertainment areas. There does not appear to be any water entry into the basement through the basement walls (horizontally), which suggests that the basement waterproofing and subsoil drainage system are in working order. A sump exists in the western plant/boiler room. A new sump pump is suggested for this sump, as pumps for each respective lift pit system. There is significant vertical water entry into the basements from ground floor slab from poorly maintained drainage and waterproofing systems as described in points above. There is substantial damage to safe doors, normal doors, door frames, soffit and wall finishes as well as stored items within the basement levels. Once the water entry issues have been resolves, the damp, doors and other architectural issues can be addressed in the basement levels. 5

6 2.8 Building Internal Brickwork The building has internal brickwork in the basements, ground floor and in the core areas on the office slabs from first floor upwards. The masonry is in general in good condition; however in the basement areas the masonry has been damaged (and hence locally cracked) from doors that have been forced open due to swollen doors, caused by water entry and lack of maintenance. The relevant doors will need to be replaced or corrected as required (possibly the frame replaced in extreme cases) before the local plaster and masonry defects can be corrected, by chipping off the problematic plaster and re-plastered as required. 2.9 Building Internal Finishes and Services. The building has internal finishes but these finishes in a poor worn state. It is recommended that the building is fully refurbished. The current office partitions can remain if required. Refer architects report in this regard Staircases The building has two central concrete staircases. The stairs cases are in good structural condition from ground floor up to roof. The staircases below ground floor are chipped and damaged, and will need to be repaired with a suitable structural patching product and refinished Structural Floor Loading Allowances Allowed For Future Use. Office and reception areas: 350kg/m 2 (Office occupancy + light weight partitions) Roof Slabs : 350kg/m2 (Office Occupancy + light weight partitions or reduced mechanical plant loading). Basement parking areas: 200kg/m2 Storage areas and safe areas in basement: 500kg/m2 Trafficable ground floor slab around the building: 200kg/m2 (No heavy vehicles or trucks, standard passenger vehicles only) Note no masonry brickwork partitions are allowed, unless verified by structural engineer. In general walls which are required to be masonry (that is bathrooms and kitchens) already exist. 6

7 3. PHOTOGRAPHIC EVIDENCE AND COMMENT: Figure 1: Southern Street façade of the building. Cladding and windows are in good functional condition, but are faded due to age. The downpipes diversions are visible and are unsightly. Figure 2: Northern Street façade of the building. Cladding and windows are in good functional condition, but are faded due to age. The downpipes diversions are visible and are unsightly. 7

8 Figure 3: Southern Street façade of the building. Cladding and windows are in good functional condition, but are faded due to age. The downpipes diversions are visible and are unsightly. Figure 4: Eastern Street façade of the building. Cladding and windows are in good functional condition, but are faded due to age. The downpipes diversions are visible and are unsightly. 8

9 Figure 5: Southern Façade Porte Cochere: Recommended that roof sheeting is renewed. Figure 6: Eastern Façade: Rainwater downpipes deviations are unsightly and need to be treated architecturally. 9

10 Figure 7: Southern Façade: Rainwater downpipes deviations are unsightly and need to be treated architecturally. Figure 8: Southern Façade drainage trench and paving above ground floor suspended slab leaks into basements below. The entire existing paving and trenches need to be uplifted, and new waterproofing system and civils works constructed on the suspended slabs. 10

11 Figure 9: Eastern Façade drainage trench and paving above ground floor suspended slab leaks into basements below. The existing paving and trenches to be uplifted and new waterproofing system and civils works constructed on the suspended slabs. Figure 10: Roof rainwater pipes appear to be in good working order, however there is no grating over the outlet and hence foreign objects can easily be washed into the pipes and block them. A new grating system must be put in place above all roof outlets. 11

12 Figure 11: Roof waterproofing has been recently replaced and is in excellent condition. Maintenance is always required to torch on waterproofing, and it is hence recommended that the silver paint on the roof is renewed every 2 years. Figure 12: The roof areas are often incorrectly used for storage of foreign objects. The roof must be cleared of all such objects on a regular basis. 12

13 Figure 13: A hoist system is available on the eastern side of the building. The system requires de-rusting and repainting and the bolted connections rechecked for integrity. Figure 14: A hoist system is available on the eastern side of the building. The system requires de-rusting and repainting and the bolted connections rechecked for integrity. 13

14 Figure 15: New solar panels have been installed on the roof. The concrete pads provided must be placed on rubber pads to ensure no damage the building waterproofing Figure 16: New solar panels have been installed on the roof. The bolts used to secure the brackets have pierced through the building waterproofing. These bolts to be removed, waterproofing restored and concrete pads provided on rubber pads to ensure no damage the building waterproofing. 14

15 Figure 17: Timber shading slats above executive balconies need to be replaced and retreated with varnish on an annual basis. Alternatively these timber elements must be replaced with maintenance free aluminum louvres or similar to architects specifications. Figure 18: Timber shading slats above executive balconies need to be replaced and retreated with varnish on an annual basis. Alternatively these timber elements must be replaced with maintenance free aluminum louvres or similar to architects specifications. 15

16 Figure 19: Southern Façade projection above roof slab level: The Copings and mosaic work have cracked and are damaged locally. Local portions of the coping and mosaic work to be replaced. Allow for 10% of the façade area, to architects specifications. Figure 20: New horizontal service penetrations through the wall compromise the water tightness of the building envelope. The air conditioner pipework shown will cause water ingress and will need to be properly sealed. 16

17 Figure 21: Skylight on northern side of building over entertainment area requires panel replacements from both a functional and aesthetic perspective. Figure 22: Skylight on northern side of building over entertainment area requires panel replacement. Photo shows damaged panel with a patch. 17

18 Figure 23: Skylight on northern side of building over entertainment area requires panel replacement. Photo shows damaged panel which is falling out of its support frame. Figure 24: Skylight on northern side of building over entertainment area has an internal gutter which is leaking into the entertainment area below. The water tightness of the skylight and the internal gutter need to be addressed. 18

19 Figure 25: Eastern Façade drainage trench and paving above ground floor suspended slab leaks into basements below. The existing paving and trenches to be uplifted and new waterproofing system and civils works constructed on the suspended slabs. Figure 26: Southern Façade drainage trench and paving above ground floor suspended slab leaks into basements below. The existing paving and trenches to be uplifted and new waterproofing system and civils works constructed on the suspended slabs. 19

20 Figure 27: Flower boxes on ground floor slab will need to be re-waterproofed as part of the ground floor slab system and the drainage system from these checked to ensure no water is trapped in the box. Figure 28: Ground floor drainage channels around the building perimeter to be re waterproofed and regarded to ensure falls to outlet positions/storm water system 20

21 Figure 29: Sliding gate track appears to be a retrofit security installation and acts as a water trap. This local depression to be eliminated by raising the gate system to be level or higher than the surrounding paving level as part of re-waterproofing the ground floor slab. Figure 30: Southern ground floor external paving to be lifted, waterproofing renewed and the paving relayed to falls. 21

22 Figure 31: Western Façade external service duct requires renewal of the waterproofing at the base of the duct and renewal of the drainage system. Figure 32: Central duct system requires renewal of the waterproofing at the base of the duct or alternatively covering the duct with a soft roof, sufficiently raised to accommodate vertical louvre panels and provision for services to exit the building through horizontal penetrations. 22

23 Figure 33: Central mechanical plant space is open to the elements and will require application of waterproofing on all vertical and horizontal surfaces. Alternatively the entire area should be covered by a soft roof sufficiently raised to accommodate vertical louvre panels and provision for services to exit the building through horizontal penetrations. Figure 34: Large horizontal opening is present in the open plant space on roof level. This opening must either be protected by a canopy or closed to seal the building envelope. 23

24 Figure 35: Water ingress from ground floor slab leaks under the external paving and planter systems has caused structural damage to the slab soffit. The waterproofing above will need to be addressed and the rusted reinforcement treated and the concrete patched with a suitable structural patching product. Figure 36: Water ingress from ground floor slab leaks under the external paving and planter systems has caused structural damage to the slab soffit. The waterproofing above will need to be addressed and the rusted reinforcement treated and the concrete patched with a suitable structural patching product. 24

25 Figure 37: Water ingress from ground floor slab leaks under the external paving and planter systems has caused structural damage to the slab soffit. The waterproofing above will need to be addressed and the rusted reinforcement treated and the concrete patched with a suitable structural patching product. Figure 38: Water ingress from ground floor slab leaks under the external paving and planter systems has caused structural damage to the slab soffit. The waterproofing above will need to be addressed and the rusted reinforcement treated and the concrete patched with a suitable structural patching product. 25

26 Figure 39: Water ingress from ground floor slab leaks under the external paving and planter systems has caused structural damage to the slab soffit. The waterproofing above will need to be addressed and the rusted reinforcement treated and the concrete patched with a suitable structural patching product. Figure 40: Internal storage rooms in the building basements have been compromised by water entry into these spaces from above. The lack of drainage and waterproofing of the slab systems above is evident on the building internal and external duct shafts and external ground trafficable and landscaped suspended floor slabs. 26

27 Figure 41: Internal storage and safe rooms in the building basements have been compromised by water entry into these spaces from above. The lack of drainage and waterproofing of the slab systems above is evident on the building internal and external duct shafts and external ground trafficable and landscaped suspended floor slabs. Safe doors have suffered damage as a result. Figure 42: Internal storage and safe rooms in the building basements have been compromised by water entry into these spaces from above. The lack of drainage and waterproofing of the slab systems above is evident on the building internal and external duct shafts and external ground trafficable and landscaped suspended floor slabs. Safe doors have suffered damage as a result. 27

28 Figure 43: Internal storage and safe rooms in the building basements have been compromised by water entry into these spaces from above. The lack of drainage and waterproofing of the slab systems above is evident on the building internal and external duct shafts and external ground trafficable and landscaped suspended floor slabs. Figure 44: Basement plant areas showing signs of water ingress from the ceiling from lack of drainage and waterproofing of the ground floor slab above. 28

29 Figure 45: Internal storage and safe rooms in the building basements have been compromised by water entry into these spaces from above. The lack of drainage and waterproofing of the slab systems above is evident on the building internal and external duct shafts and external ground trafficable and landscaped suspended floor slabs. Damp will need to be addressed once the waterproofing above is rectified. Figure 46: Internal storage and safe rooms in the building basements have been compromised by water entry into these spaces from above. The lack of drainage and waterproofing of the slab systems above is evident on the building internal and external duct shafts and external ground trafficable and landscaped suspended floor slabs. Safe doors have suffered damage as a result. 29

30 Figure 47: Basement entry doors show signs of masonry damage around the door frames, possibly from swollen doors being forced open. The walls will need to be replastered locally in these areas once the doors are replaced and no longer need to be forced open. Figure 48: Structural diagonal cracking is present in isolated locations in the basement masonry walls, most likely from long term settlement of the concrete slabs. These cracks are not cause for concern and can be regarded as local defects. The plaster will need to be patched to detail with mesh reinforcement 30

31 Figure 49: Masonry damage around the door frames is noted at various doors through the building where door hinges are problematic or doors have swollen. The cracks have occurred due to the doors being forced open. The walls will need to be re-plastered locally in these areas once the doors are replaced and no longer need to be forced open, with mesh reinforcement in the plaster. Figure 50: Internal staircases within the building are in good condition, except for the basement flights which have been chipped and damaged. These surfaces will need to be made good. 31

32 Figure 51: Internal staircases within the building are in good condition, except for the basement flights which have been chipped and damaged. These surfaces will need to be made good. The photo shows a typical stair above ground level. Figure 52: Internal staircases within the building are in good condition, except for the basement flights which have been chipped and damaged. These surfaces will need to be made good. The photo shows a typical stair above ground level. 32

33 Figure 53: Typical lift lobby on floors above ground floor: These areas are in good condition structurally, however the finishes require replacement. Figure 54: Typical office corridors above ground floor: These areas are in good condition structurally; however the finishes will need to be replaced. 33

34 Figure 55: Typical office corridors above ground floor: These areas are in good condition structurally; however the finishes will need to be replaced. Figure 56: Typical office corridors above ground floor: These areas are in good condition structurally; however the finishes will need to be replaced. 34

35 Figure 57: The basement slab construction consists of one way spanning slabs between down stand beams. The soffit condition of the slabs is good in 80% of the areas. These are numerous areas where the soffit has been damaged from water ingress from above which will require remedial patching works. Allow for patching of 20% of the ground and basement suspended floor areas. Figure 58: The basement slab construction consists of one way spanning slabs between down stand beams. The soffit condition of the slabs is good in 80% of the areas. These are numerous areas where the soffit has been damaged from water ingress from above which will require remedial patching works. Allow for patching of 20% of the ground and basement suspended floor areas. 35

36 Figure 59: It was noted that the movement joint running through the basement floor slabs has been chipped due to slight level differences which have occurred due to long term slab settlements. The chipped edges can be reinforced with edge protection, or deemed fit for purpose and left as is. Architectural guidance in this regard should be followed. Structurally either solution is acceptable. Figure 60: The boiler room is the lowest point of the building and contains the main building sump. It was noted that a basement sump pump for pumping out subsoil water/water leakages is not present and will need to be installed to mechanical engineers specifications. 36

37 Figure 61: The boiler room is the lowest point of the building and contains the main building sump. It was noted that a basement sump pump for pumping out subsoil water/water leakages is not present and will need to be installed to mechanical engineers specifications. Figure 62: It was noted in a number of locations in the basement levels that vast amounts of rubbish and old office equipment is haphazardly stored in abandoned rooms. These hoarding areas must be cleared and rubbish disposed of as it poses a fire, health and safety risk, as well as excessively loading the support structure. 37

38 Figure 63: The basement slab construction consists of one way spanning slabs between down stand beams. The soffit condition of the slabs is good in 80% of the areas. These are numerous areas where the soffit has been damaged from water ingress from above which will require remedial patching works. Allow for patching of 20% of the ground and basement suspended floor areas. Figure 64: Typical office slab construction from first floor upward: The floor slabs consist of one way spanning slabs spanning between a down stand beam system. The office floor slabs are all in good condition in areas inspected. 38

39 Figure 65: Typical office slab construction from first floor upward: The floor slabs consist of one way spanning slabs spanning between a down stand beam system. The office floor slabs are all in good condition in areas inspected. Figure 66: Typical office slab construction from first floor upward: The floor slabs consist of one way spanning slabs spanning between a down stand beam system. The office floor slabs are all in good condition in areas inspected. 39

40 Figure 67: Typical office slab construction from first floor upward: The floor slabs consist of one way spanning slabs spanning between a down stand beam system. The office floor slabs are all in good condition in areas inspected. Figure 68: Existing penetrations through down stand beams can be reused for routing new services, however no new cores are allowed through down stand beams. 40

41 Figure 72: Lift motor rooms and support systems are in good condition and are functioning. 41