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1. ELCZ LUTHERAN HOUSE STAND NUMBER 957 BULAWAYO STRUCTURAL ASSESSMENT (VIBRATIONS) Compiled by: Mbuyiseli Ncube Reviewed by: Eng. Noreen Dube (PrEng) MAY 2016 NSV &…
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  • 2. ELCZ - LUTHERAN HOUSE STRUCTURAL INTEGRITY ASSESSMENTS- VIBRATIONS MAY 2016 1 | P a g e ELCZ REFERENCE INFORMATION: Project Information: Contract reference #: Project name: LUTHERAN HOUSE STRUCTURAL SURVEY – VIBRATIONS Contact Information: ELCZ Office Details: 7 Lawley Road Suburbs Bulawayo, Zimbabwe Tel: Fax: Mobile: E-mail: NSV & ASSOCIATES REFERENCE INFORMATION: Project Information: Project reference #: 2200A.11.16 Project name: LUTHERAN HOUSE STRUCTURAL SURVEY – VIBRATIONS Contact Information: Eng. Noreen Dube NSV & Associates Suite 301 C.I.P.F Centre Jason Moyo Btwn 9th & 10th Avenue Bulawayo Tel: 09-63634 / 63636 Fax: 09-63639 Mobile: 0772 713 054, 0776 174 166 E-mail:; ,
  • 3. ELCZ - LUTHERAN HOUSE STRUCTURAL INTEGRITY ASSESSMENTS- VIBRATIONS MAY 2016 2 | P a g e Table of Contents 1. GENERAL 3 1.1. Executive summary 3 2. PART ONE: BUILDING VIBRATIONS 4 2.1. Background 4 2.2. Deliverables & possible causes 4 2.3. Existing information. 5 2.4. Site investigations 6 2.5. Discussions & Recommendations 7 2.6. Conclusion 9 3. PART TWO: STAIRCASE 10 3.1. Background 10 3.2. Existing information 10 3.3. The structural Investigations 10 3.4. Conclusion 13 LIST OF FIGURES Figure 1: General distressed staircase elevation: ....................................................................................11 Figure 2: Exposed reinforcement on beam at 2nd landing level..............................................................11 Figure 3: Cover measure on one beam ...................................................................................................11 Figure 4: Exposed rebar on landing slab ................................................................................................12 Figure 5: The rebar found on site...........................................................................................................12 Figure 6: Exposed rebar on column........................................................................................................12
  • 4. ELCZ - LUTHERAN HOUSE STRUCTURAL INTEGRITY ASSESSMENTS- VIBRATIONS MAY 2016 3 | P a g e 1. GENERAL 1.1. Executive summary Foreword: The Evangelical Lutheran Church in Zimbabwe (ELCZ) was founded in 1903 by missionaries of the Church of Sweden Mission (CSM) and African evangelists from Natal (South Africa). Zimbabwe (then Southern Rhodesia) was a mission field for the Lutheran Church in Natal. Complaints of vibrations experienced at first floor when heavy vehicles pass by were received from a tenant at the Lutheran House. ELCZ commissioned NSV & Associates in April 2016 to carry out a structural assessment of the Lutheran House in Bulawayo and prepare a Due Diligence Report. The objectives of the assessment were:  Assessment of structural drawings to understand the nature of the structure  To determine the extent of the vibrations  To identify visual defects, deterioration if any.  To identify & classify the vibrations  Assess the structural integrity of the building, and give recommendations This report is presented into two parts. Part one will focus mainly on the vibration part as explained in (i) then Part two will cover the structural assessment of staircase.
  • 5. ELCZ - LUTHERAN HOUSE STRUCTURAL INTEGRITY ASSESSMENTS- VIBRATIONS MAY 2016 4 | P a g e 2. PART ONE: BUILDING VIBRATIONS 2.1. Background The request for investigations received from the client was due to the complaints from tenants in office number 201 of incessant structural vibration. The structural vibrations were said to be experienced when heavy vehicles pass by. We visited the site to assess and ascertain these claims as well as come up with appropriate recommendations. 2.2. Deliverables & possible causes The purpose of this investigation was to assess the extent of the vibrations, the implications and give appropriate recommendations. Our assessment entailed site observations for a couple of hours in order to experience the vibrations. The engineer further interviewed tenants. The aspects listed below may cause the structure to vibrate and the ticked ones (✓) or their combination may have caused the structure to vibrate. Internal causes a. Machinery b. Elevators c. Activities of occupants. ✓ d. Addition and removal of partitions ✓ External causes a. Earthquakes b. Wind c. Blasting d. Construction operations e. Road traffic ✓ f. Interference with adjacent buildings ✓
  • 6. ELCZ - LUTHERAN HOUSE STRUCTURAL INTEGRITY ASSESSMENTS- VIBRATIONS MAY 2016 5 | P a g e 2.3. Existing information. The age of the building is unknown. The engineer found records of modifications made in 1984 and 1987. These modifications involved removal of partition walls at ground floor level. These were found to be non-structural changes. There is no other maintenance record of the building. We understand that the building was initially designed to be a multi-storey structure but was only built up to second floor level. Some drawings were obtained from the Bulawayo City Council. The drawings did not present much details leading to the conclusion that “As Built drawings” were not available. The structure is composed of a concrete frame with two floors; the roof is a concrete slab which we believe was meant to serve as the third floor. This slab is now part of the roof and is covered by galvanized corrugated roof sheets on timber trusses. We went on to carry out investigations as detailed in the following sub headings. a. Activity of occupants Annoying floor vibrations maybe caused by tenant activities. Walking, dancing, jumping, aerobics and audience participation at music concerts are some examples of prime activities that cause floor vibrations. Heating, ventilation and air condition systems if not properly isolated can cause serious vibration problems. On inspection engineers found no such activity to be occurring in the building, so this was disregarded as a possible cause of vibration. b. Addition and removal of partition walls The drawings obtained from the city council show addition of partition walls and provision of cold room around 1987 to allow for a butchery occupation. We found all these changes to be non-structural frame modifications. Thus this is will be ruled out as a possible cause. c. Interference with adjacent buildings Vibration of a building or associated activities can cause vibration in a structure next or adjacent to it. Next to the Lutheran house is Matopo Book centre. We took interviews on tenants in the building and found that there were no vibrations experienced.
  • 7. ELCZ - LUTHERAN HOUSE STRUCTURAL INTEGRITY ASSESSMENTS- VIBRATIONS MAY 2016 6 | P a g e d. Road traffic vibrations Movement of vehicles on a road with irregularities such as in the road surface e.g. potholes, cracks, uneven manhole covers induce dynamic loads. These loads generate stress waves which propagate through the soil, eventually reaching the foundations of adjacent buildings and causing them to vibrate. Traffic vibrations are mainly caused by heavy vehicles such as buses and trucks. Light vehicles rarely induce vibrations that that are perceptible in buildings. 2.4. Site investigations We visited site and spent time in office 201. The purpose was to experience and appreciate the nature of the vibrations. The investigations were carried out between 0800hrs to 1200hrs. During the time we spent there three heavy trucks passed by. We did not experience these said vibrations. We also carried out interviews on the tenants to ascertain their experiences. OFFICE NUMBER FLOOR NO. INTERVIEWEE FINDINGS Shop No. 2 Ground floor Sakhile Sibanda No vibrations reported 102 First floor No vibrations 117 First floor Mrs Sibanda No vibrations 104 First floor Miss Sibanda No vibrations 201 Second floor Tshuma Vibrations felt during a thunderstorm 201 Second floor Madawu Vibrations felt when heavy trucks pass 202 Second floor Roof leakages 203 Second floor Roof leakages no vibrations
  • 8. ELCZ - LUTHERAN HOUSE STRUCTURAL INTEGRITY ASSESSMENTS- VIBRATIONS MAY 2016 7 | P a g e 2.5. Discussions & Recommendations Our professional opinion is that the building vibrations are results of a possible periodical vibrations of the adjacent pavement induced by heavy vehicle movements. This however is subject to pavement investigations. Building vibrations caused by road traffic are not a health and safety concern; they are more of a problem of annoyance. Vibrations may be unacceptable to occupants because of annoying physical sensations produced in the human body, interference with activities such as conversation, rattling of window panes and loose objects, and fear of damage to the building and its contents. Experience has shown that people are likely to complain if vibration levels are only slightly above the perception threshold, the major concern being fear of damage to the building or its contents. The tolerance level varies widely from person to person and from area to area. Our investigations indicate that only two people felt the vibrations. These vibrations can cause cracks in walls and ceilings, in which case we did not observe any such cracks. However, vibration levels are rarely high enough to be the direct cause of this damage, though they could contribute to the process of deterioration from other causes. Building components usually have residual strains as a result of uneven soil movement, moisture and temperature cycles, poor maintenance or past renovations and repairs. Therefore, small vibration levels induced by road traffic could trigger damage by “topping up” residual strains. Consequently, it is difficult to establish a vibration level that may cause building damage. In some cases, when a building is subjected to vibration for many years, fatigue damage (i.e., that caused by repeated loading) may occur if the induced stresses in the building are high enough. In addition to damage caused directly by vibration, indirect damage may result from differential movements caused by soil settlement due to densification. Loose sandy soils are particularly susceptible to densification when subjected to vibration. Based on the above discussion our recommendation is that a scheduled annual inspection be carried out on the building to ascertain if these vibrations get worse.
  • 9. ELCZ - LUTHERAN HOUSE STRUCTURAL INTEGRITY ASSESSMENTS- VIBRATIONS MAY 2016 8 | P a g e Table 1. Comparison of vibration levels (mm/sec2, rms) induced by a bus and a truck, to demonstrate the effect of different speeds on induced vibrations. Location 25 km/h 50 km/h Bus Truck Bus Truck Ground in front of house 20.5 19.9 64.5 33.2 External foundation wall 11.2 10.1 30.9 15.7 Mid-point of floor in 1st storey 20.3 20.8 62.9 30.1 Mid-point of floor in 2nd storey 35.0 37.3 96.2 46.7 From table 1 it is seen that the second floor is the one that experiences the highest vibrations when a car travelling at an approximate speed of 50km/h interacts with an irregularity on the road surface, and hence could explain the fact as to why only the tenants on the second floor are the ones that filed the complaint, and also that if cars are travelling at a minimal speed, the vibrations are likely to be less.
  • 10. ELCZ - LUTHERAN HOUSE STRUCTURAL INTEGRITY ASSESSMENTS- VIBRATIONS MAY 2016 9 | P a g e 2.6. Conclusion Tenants may complain about vibrations if the levels are only slightly above the perception threshold, the main concern being fear of damage to their property and discomfort. Building damage may occur but it is unlikely to be caused solely by the vibrations themselves. Reducing vibrations to an acceptable level could be difficult and expensive. For existing buildings, the most practical remedial measure is road maintenance. For new developments, increasing the distance between buildings and roads, improvement of soil structure and in ground pile barriers could prove effective. During the subsequent yearly inspections, should the size of vibrations increase, we would recommend that the client approaches the City of Bulawayo and attempt to investigate and remedy road pavement weaknesses. Structural Engineer’s opinion is that the structure is safe for occupation and vibrations are not an immediate threat to human life or occupation.
  • 11. ELCZ - LUTHERAN HOUSE STRUCTURAL INTEGRITY ASSESSMENTS- VIBRATIONS MAY 2016 10 | P a g e 3. PART TWO: STAIRCASE 3.1. Background The purpose of this structural survey was to ascertain and report on the extent of structural defects on the staircase and give recommendations for the staircase’s general rehabilitation. The assessment of the structure involved field and structural analysis in order to recommend appropriate and cost effective restoration measures. The structural review conducted mainly focused on the:  Age of the structure  Causes of staircase structural cracks  Recommendations for rehabilitation 3.2. Existing information Prior to the commencement of visual inspections, the engineer sought a set of the building’s structural layout plans and details. The drawings obtained from the city council did not provide any detailed structural information. 3.3. The structural Investigations The stair case is of reinforced concrete with brick masonry guard rails. Generally the staircase structure shows signs of distress. Cracks were observed at all levels, a significant portion of the staircase reinforcement is exposed.
  • 12. ELCZ - LUTHERAN HOUSE STRUCTURAL INTEGRITY ASSESSMENTS- VIBRATIONS MAY 2016 11 | P a g e Figure 1: General distressed staircase elevation: The image below shows a beam at second landing level. The beam has cracks at its soffit. These cracks have resulted in exposed reinforcement. The average cover to rebar is 15mm & this is far less than recommended minimum of 25mm. Figure 2: Exposed reinforcement on beam at 2nd landing level Figure 3: Cover measure on one beam
  • 13. ELCZ - LUTHERAN HOUSE STRUCTURAL INTEGRITY ASSESSMENTS- VIBRATIONS MAY 2016 12 | P a g e Figure 4: Exposed rebar on landing slab The extent of exposure of the reinforcement is at a critical level. We approximate 10% of the staircase reinforcement is exposed. The cracks shown in figure 3 will continue to increase. Figure 5: The rebar found on site Figure 6: Exposed rebar on column We recommend that the rebar and concrete surface be repaired/ rehabilitated as detailed below: a. Fix props and supports around the location to be repaired, especially in the surroundings of damaged columns and beams. b. Delimit the area of damage c. Break beyond the delimited area until reaching sound concrete and steel.
  • 14. ELCZ - LUTHERAN HOUSE STRUCTURAL INTEGRITY ASSESSMENTS- VIBRATIONS MAY 2016 13 | P a g e d. Saw-cut 20mm deep in 90° angle the perimeter of breaking, in order to avoid feather edges. e. All weak, damaged and easily removable concrete should be chipped away. If the re-bars are only partially exposed after all unsound concrete is removed, it may not be necessary to remove additional concrete to expose the full circumference of the reinforcement. When the exposed reinforcement steel has loose wrap, corrosion or is not well bonded to the surrounding concrete, the concrete removal should continue until a clear space of 15 to 25 mm is created behind the reinforcing steel. f. Clean steel reinforcement with wire-brushing, sand blasting or chemical rust remover. g. In cases where the reinforcing bars are corroded and have lost more than 25% of their diameter, they have to be cut and removed. In such event, removed steel bars should be replaced with new steel bars of the same diameter either by respecting the overlap length or by welding 100 mm length to the existing steel. h. Remove dust by air blowing and wash with clean water to achieve a Surface Saturated Dry (SSD) area. i. Protection of rebar against corrosion. Rebar can be protected against corrosion with a highly alkaline product or a zinc rich product that delays the aggressive elements attack on steel. Examples of such products Conrep.370 PF and Conrep.501 ZRP. j. Concrete mix of approved mix design must be applied using an approved bonding agent. k. Proper curing should be performed. 3.4. Conclusion The staircase structure investigations indicate that a critical & immediate attention is required. The structure will continue to deteriorate to risky levels if not rehabilitated. The debris falling from the cracked positions poses an injury threat to occupants & passer byes. The extent of rebar corrosion cannot be known as it is covered in sections. Excessive corrosion can weaken reinforcement and result in structural failure. 3.5 Recommendations We recommend that the client appoints the structural engineer to prepare specifications for rehabilitation of the staircase & ancillary structures. Contractors can then be invited to quote for the remedial works under the strict supervision of the engineer.
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