HOW TO AVOID BUILDING STRUCTURAL FAILURES



BUILDING STRUCTURAL FAILURES

In spite of the best practice and attention during the structural analysis, design, detailing and construction of buildings, it is unfortunate that failures do occurs in practice. It may be small or big. Failures of members or structures may occur due to errors in the analysis, design, construction and maintenance of buildings. One can learn a lot from failures of structures. When a member fails (say, cracks), it is trying to tell the structural engineer something about behaviour, about its deficiency on several aspects. The structural engineer needs to understand the language of the structure and analyze the cause of the deficiency and then suggest a suitable remedy so that the member is made good and strong again.

ANALYSIS AND DESIGN ERRORS


HOW TO AVOID BUILDING STRUCTURAL FAILURES
Case-1: In a fertilizer project, a lime storage underground building was to support a huge amount of limestone, for which the equivalent design uniformly distributed load was given in kg/sq.m on conversion to foot-pound system, used in those days, the value of load was wrongly taken at 300 lb/sq.ft (i.e. 1500 kg/sq.m), while the actual loading worked out to be 3000 lb/sq.ft (15000 kg/sq.m). The designer thought that 300 lb/sq.ft to be quite a high value and the structure was designed and structural drawings were prepared and checked and these along with a copy of the calculations were sent to the site. At the site, footing bars and wall steel were erected in position. At that stage, the design office's representative at the site spotted the error in the loading and the work was stopped at the site.
Remedial measure: The design was corrected, keeping the concrete thickness same as before, so that shuttering work at the site remained unchanged. Steel requirement was changed. Additional steel bars were provided along with the previous steel arrangement. The structural drawings were accordingly revised and the work was completed at the site. The design error was spotted at the site in nick time and a major fault was this avoided.
HOW TO AVOID BUILDING STRUCTURAL FAILURES
Case-2: In a cinema building, a parapet of large depth above the roof level was proposed by the architect. The structural engineer by his knowledge, thought of providing a channel section in order to save the weight of materials and thereby achieve economy. After a few days of construction, the channel section, with its shear centre outside the section, was seen to be rotating outside and large cracks were formed in the concrete parapet. Had been a regular section (b x d), this rotational effect would not have taken place.
Remedial measure: The channel shaped concrete parapet was dismantled and a rectangular parapet was built, which is standing since then without any problem.

HOW TO AVOID BUILDING STRUCTURAL FAILURES
Case-3: North-light folded plate over a workshop was built and after sometime, the glass panes in the glazing were reported to be breaking on and off. The structure was propped from below and the site was visited and the drawings were studied. The problem was in the traverse design and its arrangement. The lower part of the traverse was made of reinforced concrete and its upper part was made in brick. The entire traverse should have been made reinforced concrete, so that, the folded plate is held in shape at all points along its cross section. Because of the brickwork, the upper portion of the folded plate was opening out, pressing on the glazing and breaking its glass panes thereby giving ample warning to those who would listen and understand!
Remedial measure: The structure could have been repaired by removing the brickwork and making the full traverse in the reinforced concrete. But, an alternative steel solution was adopted at the site, whereby, the folded plate is acting as just the covering slab resting on steel trusses, which were introduced to support the existing folded plate.
HOW TO AVOID BUILDING STRUCTURAL FAILURES

Case-4: In a single-storey auditorium building cracks developed in the supporting brick piers above the roof. The long-span roof consisted of a waffle slab resting on brick piers all around the periphery. The deflected shape of the roof structure pushes up the parapet above the roof, causing cracks in piers on the outside above the roof level. This type of crack formation cannot be avoided.
Remedial measure: A groove was made at this level to accommodate the separation of the parapet masonry from that of the supporting brick pier. The deflection of bending member is a natural phenomenon and this sort of cracking is not structurally harmful.
HOW TO AVOID BUILDING STRUCTURAL FAILURES

Case-5: In a single storey house of a doctor, the canopy slab at the level of the main roof was found to be sagging. The waterproofing over the roof was already done. On inquiry, it is found that no structural engineer was engaged for design, rather a novice had done the structural design of the house. The client being a doctor himself creating the situation he was in.
Remedial measure: Two I-joists were introduced as shown in figure under the slab, supported on the existing brick walls and these stabilized the cantilever canopy slab. The client had to spend much more than what he saved by appointing a novice.
HOW TO AVOID BUILDING STRUCTURAL FAILURES
Case-6: In a multi storey building, there was a floor of 40'0" span. It consisted of closely spaced ribs of 40'0" span with the topping slab. The depth of the ribs was kept at the minimum required of      l/20 = (40 x 12)/20 = 24". On this floor, a few residential units were built by means of 115 thick brick walls. When the building was occupied, after sometime, there were many cracks in the 115th brick walls, while the supporting slab and ribs were absolutely crack free. The cracking in brick walls is caused by the deflection of the ribbed one-way slab. At the center of span, the deflection is more while near the supports it is less. Further, it is less on the front and more on the back sides. Due to this variation in deflections, brick walls get cracked as these are brittle and cannot absorb these deflections.
Remedial measure: After a certain period of time, these cracks were repaired assumed that most of the deflection of slab had already occurred.
HOW TO AVOID BUILDING STRUCTURAL FAILURES

Case-7: A workshop building with a flat roof failed suddenly. The roof consisted of red sandstone slabs, resting on inverted T-sections, which were resting on I-section joists. The I-joists were resting on R.C.C columns. On the stone slabs earth will be laid to slope for roof drainage. When the earth was being laid on top, the roof suddenly collapsed. Luckily there was no casualties. On detailed analysis, it was found that I-joists failed by lateral buckling as inverted T-sections were only resting on I-joists, these should have been welded to the I-joists.
Remedial measure: The twisted shape of the I-joists of the failed roof also tested for correctness of this finding.

DETAILING ERRORS
HOW TO AVOID BUILDING STRUCTURAL FAILURES
Case-8: In a hostel building, there was a cantilever balcony along the rooms which also turns across at the end of rooms. When the shuttering of the balcony slab was removed, it was found that the corner (A) on the diagonal was sagging. This was due to the fact that no extra diagonal top bars were provided along the diagonal.
Remedial measure: The sagging portion of the slab at the corner was cut off and the shape of the balcony in plan was changed.
HOW TO AVOID BUILDING STRUCTURAL FAILURES
Case-9: The columns of a cantilever platform shed were developing horizontal cracks at a fixed height above the ground level. When shuttering was removed, these cracks were appearing slowly in all columns at a fixed height. Immediately, the frames were propped at the free end of long arms and after studying the design and drawing it was found that laps in column bars were provided at a distance of 35x dia of bars as it was done normally for bars in compression. But in this case, the cantilever moment is very high and the bars in this side were clearly in tension, so lap length of 45 x dia of bar was required (as per old code).
Remedial measure: It was suggested to expose the bars near about the crack line and weld the lap bars with the column bars and re-concrete that portion. After the curing period, the props on the free ends of long cantilever arms were removed and the cracks did not appear again. The correct diagnosis led to the correct remedial measures.
HOW TO AVOID BUILDING STRUCTURAL FAILURES
Case-10: In a canteen building, a vertical crack at midspan was observed in a deep beam over the service counter. The drawing of the beam showed no side face steel. At least two bars on each face of the beam should be given.
Remedial measure: The stirrups at those locations were exposed, bars welded and the re-concrete was done. The cracked portion was repaired. Provision of side steel in deep beams was not mandatory in the previous code, but now it is mandatory.
HOW TO AVOID BUILDING STRUCTURAL FAILURES

Case-11: In a workshop building, cylindrical shell roof was provided with steel arrangement as shown in figure. After completion of the building extensive thin cracks were observed in the shell roof from inside. After a thorough study of the analysis and design of the shell roof, it was concluded that transverse steel should have been put on both faces of the shell thickness all through.
HOW TO AVOID BUILDING STRUCTURAL FAILURES
HOW TO AVOID BUILDING STRUCTURAL FAILURES

Case-12: A serious failure occurred due to a detailing error in ramp slab, which was cantilevered out from a central wall shaft. The ramp was separated from the adjoining floor by an expansion joint. The span of the cantilever was 2.35m and section X-X gives the steel arrangement as given in the relevant structural drawing. The embedment (anchorage) length of the bottom 10mm bars was given 300mm. As the word 'TYPICAL' was written in the drawing, the embedment length of top 16 bars was also provided 300mm at the site, instead of the required 700mm. Because of this detailing error, when the shuttering was removed slowly a crack was forming at the junction of the slab with the wall.
Remedial measure: Immediately the free edge of the ramp was propped and a steel beam with steel columns were permanently provided to support the free edge of the ramp slab, so that the final behaviour of the ramp slab was simply supported with a span of 2.35m, for which 10 nos @200c/c bars at bottom were sufficient. The lesson from this failure is that, for cantilever slabs and beams, the main bars should be anchored and their embedment lengths should be separately and clearly mentioned in the drawings.

CONSTRUCTION AND MAINTENANCE ERRORS

Case-13: A petrol pump station structure was a hyper shell structure supported on a single column. This structure was built in accordance with a standard drawing and cracks had developed on roof top as shown in plan. The structure was propped at free edges. On visiting the site, it was felt that the contractor had not been able to understand the supplied drawing. He put more steel on the free edge and less on the column side, unlike shown correctly in the drawing.

HOW TO AVOID BUILDING STRUCTURAL FAILURES
Remedial measure: After checking it was decided that demolishing would be the best choice. And, asked the contractor to demolish the hyper shell and redo this work again. However, before he could do it, the structure collapsed one night due to vibration of a passing truck. Luckily, there was no casualty. This failure can be ascribed as the incompetence of contractor and also to the lack of supervision at the site.

Case-14: A single storey bungalow was under construction. The neighbouring plot was empty and its owner started digging foundations for his building deeper than the foundations of the bungalow. The excavated footing trenches were kept open for long time and during this period, it rained heavily, as a result the end wall of the bungalow rotated and there were large cracks in the ground floor also.
HOW TO AVOID BUILDING STRUCTURAL FAILURES


Remedial measure: The further excavation at that corner was stopped and the surrounding of bunglow was protected with proper supports, so that further deterioration could be avoided. With proper precautions the excavation near the existing wall was done in parts in a sunny day and quickly the work was completed and back filled. For protecting the existing property, one should not excavate near the existing wall. One should maintain at least 3'0" distance from the existing wall and the rest of the plot can be dug out as required part by part and the work is to be completed quickly, so that the existing property is not damaged.

Case-15: A retaining wall, which was supported a high ground with a swimming pool, was observed to be tilting outwards. On visiting the site, it was found that water was leaking from the swimming pool and it was exerting extra pressure on the retaining wall.
HOW TO AVOID BUILDING STRUCTURAL FAILURES
Remedial measure: The remedy was suggested to drill holes in the retaining wall and insert pipes  to act as a weep holes, so that water pressure on the wall can be reduced. This added to the safety of the wall.

Case-16: An oil tank roof failed. It was consisted of radial trusses and circumferential trusses with a top steel plate. The radial trusses were supported on the steel tank walls. The client wanted to do cement plaster on the roof. That proved to be excessive load and the joint of the radial truss with vertical steel wall failed.
HOW TO AVOID BUILDING STRUCTURAL FAILURES


Remedial measure: The roof was done without cement plaster.


Case-17: A well planned bungalow was designed by an architect and structural drawing was prepared. When the work started at site, neither the architect not the structural engineer was employed by the client. The client asked the contractor to had a bea free roo. Contractor in his wisdom, thought beams were not required, so he provided two bars top and bottom at all beam locations. The slab was casted and then shuttering was removed. Cracks started at many locations. On site visit, it was seen that slab panels were large and balcony slabs also large spans. On all critical sections, the cracks were bound to occur due to omission of beams.
Remedial measure: Those beams were again provided by suitably breaking the concrete and welding of bars with the old ones, then re-concreting and curing these new concrete patches in the slabs and beams. Though the client had to spend a good amount, but the structure was set right.

Case-18: A multi-storey apartment building was constructed in seventies. The plateau on a hill, on which the building was constructed was about 12m above the the surrounding area. Foundations were provided after soil investigation and there was no problem for the main building. The owner wanted to construct a single storey garage block. The structural engineer decided to support one end of the garage block on the existing old 12m high stone masonry wall as shown in figure. During rains, the entire garage block toppled and rested on a building 12m below on the ground. This failure was due to the failure of old retaining wall during rains.
HOW TO AVOID BUILDING STRUCTURAL FAILURES
Case-19: A single storey factory building with R.C.C roof was constructed in seventies. The 12m roof span was casted earlier. Later 15m span was casted. When shuttering was removed, 15m span was collapsed. It was noticed that concrete in the bottom layer of 15m span beam was honeycombed and it did not offer any bond to the reinforcement and the structure collapsed. As the collapsed started, top 2 height of the immediate column was pulled in (towards 15m span) and failed in bending due to the pull of the collapsing beam.


HOW TO AVOID BUILDING STRUCTURAL FAILURES
Remedial measure: It was recommended that for beams with spans greater than 6m, lapped bar should at least be tack-welded to avoid this type of failure.

Case-20: A reinforced concrete framed factory was being extended upwards. The beams developed cracks as these were not propped from below, when the upper storey was extended. The load of shuttering, the weight of concrete and the erection loads exceeded the load capacity of the existing beams.
Remedial measure: Immediately, the beams were adequately propped. This failure is caused by laxity of the construction stuff.

Case-21: In a running steel plant, a roof shed collapsed due to overloading caused by the dust deposition on top. Dust contains heavy iron particles too. This is maintenance failure.

Case-22: A 30m span storage hall (stockyard) building used to be provided in the earlier plants with a provision of 10 tonne lifting capacity grab crane. To feed materials to the various hoppers, the crane operated continuously for 24 hours. In many plants, there was excessive deflection of columns during crane operations and the crane used to get derailed. In one plant, due to excessive deflection of columns the roof collapsed.
HOW TO AVOID BUILDING STRUCTURAL FAILURES
Remedial measure: After study of the various failures in similar plants, the following decisions were taken:

  1. Crane horizontal surge for high frequency operated grab cranes should be 10% of the maximum static wheel load per wheel.
  2. After observing such failures, the plant suppliers specified relative deflection between adjoining columns in longitudinal direction to be limited to 2cm. This should, however, be worked out on the basis of limiting clearance between the rail and wheel.
  3. The design will be governed by the deflection limitation for serviceability of crane and not by stress considerations.





HOW TO AVOID BUILDING STRUCTURAL FAILURES
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Green Environment

Hi, I’m Gobinda Burman (Green Environment). More than 27 years in the field of Building Construction industry, I’ve completed many high-rise building projects successfully. I have got the opportunity to learn and solve the critical practical problems related to building construction. I love to share my knowledge with those people who wants to build their own home and the budding civil engineers willing to build their career in this field..

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