Reinforced Concrete Construction Failures Exposed by Earthquakes

Transcription

1 HUYS ADVIES Reinforced Concrete Construction Failures Exposed by Earthquakes Examples of design mistakes in reinforced concrete constructions Report by: Sjoerd Nienhuys Architect, Engineer Report date: May 2010 Examples in this report from: Ecuador, Nicaragua, Indonesia and Pakistan. Reinforced Concrete Construction Failures, May 2010

2 TABLE OF CONTENTS 1. INTRODUCTION LEARNING FROM MISTAKES ECUADOR, ESMERALDAS MANAGUA, NICARAGUA ACEH, INDONESIA BALAKOT, PAKISTAN RECONSTRUCTION...17 ABSTRACT After earthquakes it becomes very visible what types of building construction have withstood the forces of the earthquake and which did not perform adequately. Analysing the nearly collapsed and broken structures gives a good insight in the possible architectural and engineering design mistakes, faults in the detailing and the mismanagement of the construction by the building contractors. For reinforced concrete construction, mainly inadequate column designs and over-weight structures are the cause of fatal building failure and related human victims. Heavy and stiff floor constructions are disadvantageous for the overall strength and ductility of the reinforced concrete buildings. The paper gives 35 picture examples are given from Ecuador, Nicaragua, Indonesia and Pakistan. Key words: earthquake, building design, failure, columns, reinforced concrete, stirrups, pancake. All pictures by the author: Sjoerd Nienhuys, Architect, engineer consultant@nienhuys.info More information on earthquake engineering on Reinforced Concrete Construction Failures, May 2010

3 1. INTRODUCTION Only after the occurrence of an earthquake it can be seen if the buildings have performed adequately according to their planned design. The design criteria, however, may be different for each type of building, especially when no binding national Code exits that defines the minimum strength. The American Concrete Institute ACI-318 earthquake resistant building code is widely copied and adapted into national standards of South American countries. Currently the ACI-318 has a new updated version (2008) improving again on the version of 1999, but many countries in the worlds major earthquake zones have older versions of this code, and local adaptations. Yet, when the buildings are designed and constructed according to these codes, they will most likely not fatally collapse with an earthquake of a magnitude 7 on the Richter scale. The recent earthquake on 12 January in Haiti (Léogâne near Port-au-Prince) had a magnitude of 7 Richter in the epicentre. With an estimated depth of 13 km under the city of 2 million inhabitants it resulted in massive damage and somewhere between 50,000 to 230,000 causalities. The number has been very uncertain because of a failing government infrastructure. The latest large earthquake occurred on 27 February 2010 in Chile (Maule region, Cañete) had a magnitude of 8.8 Richter in the epicentre being 115 km from the city of Concepción, with a depth of 35 km, being one of the largest earthquakes ever registered worldwide. The death toll in Chile however, was approximately 300, being more than doubled by the following tsunami to over 708, and counting. The differences in death tolls are significant and caused by the following characteristics: # Haiti, 12 January 2010 Chile, 27 February Force earthquake 7 Richter Force earthquake 8.8 Richter = 500 x stronger 2 Depth 13 km (shallow) Depth 35 km 3 Right under the village Léogâne (10,000), and only 25 km from capital Port-au- Prince with over 2 million inhabitants. Concepción at distance of 115 km. More than 50% of causalities caused by tsunami crushing into small coastal villages. 109 km from Talca aftershocks 4 Richter and greater with Maximum aftershock 6.2 Richter two of magnitude 5.9 Richter. 5 Over 1.2 million people homeless Over 2.1 million people homeless 6 Poor quality houses, not build according to earthquake code. Better quality houses, many build according to earthquake codes. 7 Many single storey adobe houses in town, having a loose structure and large mass. House destruction along the coast also by tsunami flood. 8 No exist government control on building practices and substantial corruption. Government control on designs and reasonable government control with little corruption. 9 No history of large earthquakes and no information available on better design. History of very large earthquakes in same region and available documentation with pictures. 10 Large amount of informal building without involvement of architects and engineers. Training of architects and engineers include the application of the earthquake design code. Although the earthquake in Chile was 500 times stronger, the larger depth and the lesser population nearby are part of the lesser number of causalities. However, the largest difference is the better building construction practised in Chile. This is a result of one of the largest recorded earthquakes ever recorded in the same region in 1960 and a functioning government structure as opposed to Haiti which is a failed state for the last half century. The failed state situation causes lack of training of engineers and architects and a total lack of control on what was/is being build. This paper reviews 35 pictures taken by the author from Ecuador, Nicaragua, Indonesia and Pakistan. Reinforced Concrete Construction Failures, May

4 1.1 LEARNING FROM MISTAKES Any learning process has different components through which learning takes place. School learning may be based on book knowledge, theoretical explanations and study, but most people learn more from real examples and learning by doing. Seeing is also much more educative than just reading, reason for which the illustration of a topic is of great importance to the learning process. Analysing post earthquake pictures does vividly teach about what designs were faulty and why. Unfortunately, that cannot be said from the structures that were not damaged because from the outside little can be seen. Only the study of the drawings and calculations can determine why a certain structure did not fail, and while neighbouring structure were damaged or totally collapsed. In particular those constructions that are at the point of total failure are interesting because they present themselves as a freeze frame during the process of collapsing. In the following paragraphs some picture material is shown of earthquake damage and commented upon. Also some information is provided about constructions that have either good or bad designs. The information is not at all exhaustive or complete in all details, but it provides some very common examples that can be found in many cities in earthquake zones. Buildings are primarily designed to carry their own weight and the live load caused by occupants. The own building weight is often the most determining factor in the design. That weight is vertical. Small tremors that have predominantly a vertical vibration P or the vertical component of the Rayleigh movement, are easily withstood by most of the buildings. Buildings however, that are located sideways away from the epicentre will receive a lateral rocking type force S from the quake, moving the building forward and backward which is often the cause of major damage. Buildings are subject to a combination of the waves indicated in the picture, but the effect will depend on the soil structure and distance from the epicentre and hypocentre. The wave length (horizontal component of the Rayleigh type wave) and the time between forward and backward movements will increase with the distance from the Epicentre. With increasing distance from the epicentre the wave amplitudes will diminish. The earthquake resistant building codes take into consideration the balance between the risk of a heavy earthquake 7 to 8 Richter occurring in a given location, and the very high economic cost of building everything extremely earthquake resistant. The code recommends minimum construction standards to avoid total collapse but allows people to evacuate, even if the building is a total loss. Building with brick and concrete to withstand a Richter 8 earthquake without damage is economically very costly; the alternative is a very lightweight and ductile structures. The force of an earthquake on a building is directly related to its mass. Sjoerd Nienhuys Architect, engineer Reinforced Concrete Construction Failures, May

5 2. ECUADOR, ESMERALDAS Reinforced concrete is a so called modern building material in the eyes of many people, especially rural people and those living in villages, because they see large town buildings going up in reinforced concrete. However, reinforced concrete is very heavy and therefore not a suitable material for building lightweight. Secondly, the quality of the reinforced concrete depends on the design and the location of the reinforcement as well on the cement and water quantities, aggregates, casting method and the curing. With a good design and poor quality work implementation, the concrete does not have the required strength and the planned interaction between the reinforcement steel (stress resistance) and the concrete (press resistance) will be disturbed, resulting in a low structural strength. People like to build in reinforced concrete because the material has the image of durability due to its use in expensive buildings in large towns. Many different aspects can lead to low quality and failure of reinforced concrete buildings. 1. The designs are architecturally not always appropriate for high risk earthquake areas. In some countries the architects do not have adequate design training and rely on the engineers to fix their designs according to the strength requirements. 2. The engineers have not always indicated the correct reinforcements at the correct positions. 3. In Latin America and other countries there is too often no coordination between the architects and engineers, but the engineer is made responsible for the correct design strength. 4. The drawings of columns and other reinforcements are not always individually detailed. 5. For building components the architects and draughtsmen do not detail the reinforcement or make on each drawing detailed charts for the steel cutting and bending. 6. The small contractors and work supervisors do not always understand the drawings provided. 7. Corrupt contractors may change the steel quality, dimensions or leave out reinforcement. 8. Poor contractors may use inadequate quality of aggregates such as sand (dirty), stones (weak), and water (salty) and cause improper mixing (by hand) or add too much water (W/C factor). 9. Poor quality formwork and insufficient cleaning of the formwork may cause dirt and binding wire to remain, spacers improperly placed, and eventually rust forming on the long term. 10. Poor quality or sloppy contractors may use faulty casting techniques that cause leakage from the formwork and honeycomb concrete with aggregate pockets. 11. Poor quality of casting work will minimise vibration, leaving air inside the concrete. 12. Poor quality or corrupt contractors as well as unaware private builders may inadequately cure the fresh concrete by keeping it insufficiently wet and for insufficient time. This is very often the case in warm, hot and sunny climates. 13. Municipal control is often lacking on the design drawings whereas in many countries the design drawings are unverified and rubber stamped by corrupt government employees. 14. Municipal or government inspection personnel does not always adequately supervise the work of the contractors on the job, or just before the casting of concrete takes place. 15. No test cubes are made from the actual concrete that is used in the work, or the test cubes made are properly cured, whereas the concrete cast is not adequately cured. The above list of 15 points is the sad result of lack of standards, lack of education and a failing supervision system, several or all of which can be regularly found when inspecting post earthquake damage. It was one of the results of the author s investigation of the Esmeraldas earthquake in 1976, and is most likely the case related to many damages in the Haiti earthquake. The above list of 15 points also shows the possible dangers in the use of reinforced concrete, and it illustrates that in the construction process, control is required for every step. A particular problem of reinforced concrete is that once it is cast, it is difficult to assess for a citizen the quality if the concrete and even more difficult to assess the quality of the reinforcement inside. Seeing concrete columns and beams on the outside does not guarantee a good quality construction, unfortunately some reinforced concrete buildings are a simple death trap during an earthquake. Reinforced Concrete Construction Failures, May

6 The earthquake of 9 April 1976 in Esmeraldas, Ecuador had an estimated force of VI on the modified Mercalli scale or approximately 5.5 to 6 on the Richter scale. Some damages depicted here are from reinforced concrete buildings that were in their construction phase. Because of the available reproduction possibilities in 1976 the most significant pictures were drawn in pencil. Picture 10. Esmeraldas. This was an line of shop buildings, being fully pancaked due to failure of the supporting column structure. The building was realised without the consideration of any existing earthquake construction code and had insufficient shear walls inside to support lateral forces. Picture 11. Esmeraldas. The same building close up from the side showing the thickness of the solid reinforced concrete floors. The thickness of the 20 cm solid concrete floor was increased by <<<<< an 8 cm thick layer of cement topping, causing the floor and roof to weigh more than 670 kg/m 2. With a size of 9 x 30 m or 180 ton per floor, this is causing a massive horizontal load during an earthquake. Only very well designed shear walls can resist such a force. Picture 12. Esmeraldas. A line of new apartment buildings totally flattened or pancaked as a result of the failure of the columns. The block was in its construction phase and the contractor had not realized the infill walls on the ground floor, while the first floor was already loaded with masonry for facades and separation walls. In this case the planning or the construction phases in the building process had not considered that the area is a notorious earthquake zone. Reinforced Concrete Construction Failures, May

7 Picture 13. Esmeraldas. The same building complex, dropped down one storey. The upper storey did not totally collapse because several cement block masoned infill shear walls have been put in place. Avoiding this kind of damage requires the realization of shear walls in two directions before the next floor is being constructed. An option is to complete the stair wells first if these are part of the structural design. Picture 14. Esmeraldas. This section just did not pancake but will do so with the next aftershock. The weakest points in the structure are the maximum moment areas in the columns. The concrete crumbled as a combination of the large forces and poor quality. Lack of confinement or caging of the broken concrete makes the steel reinforcement useless. Picture 15. Esmeraldas. The lack of confinement of the broken concrete causes the pebbles to fall away, by which the interaction between steel and concrete is lost. This is invariably the major cause of the collapse of reinforced concrete constructions. Building earthquake resistant means that although the construction (here the concrete) is broken the building remains standing without collapse. This way people can still evacuate the damaged construction. Reinforced Concrete Construction Failures, May

8 Picture 16. Esmeraldas. The lack of adequate anchorage between the support beam and the column allows the beam to be disconnected from the column; it also reduces the confinement of broken concrete. It is possible that the design drawings did not specify the anchorage of the reinforcement bars, or that the contractor did not put them according to correct drawings. Picture 17. Esmeraldas. The sketches were made from pictures and demonstrate the lack of anchorage and the lack of stirrups found. These kind of details indicate the need for precise control of the design as well as on-the-job verification of the reinforcement BEFORE the concrete is cast. The minimum anchoring length of the bars linking beams to columns is specified in all Reinforced Concrete Codes and is minimal 30 cm. The vertical sections of the reinforcement bar (sketches below) should be minimal 12 x the bar diameter. Technical drawings should be verified by qualified engineers. Reinforcement drawings should have detailed cutting and bending schedules that can be followed by the iron workers. Before the concrete is cast in situ, a detailed inspection should be realised of all bars fitted in place, as well as the quality and cleanliness of the formwork. Reinforced Concrete Construction Failures, May

9 Picture 18. Esmeraldas. Another reason of the collapse of the buildings was the poor quality of the concrete casting, in some cases exposing too large aggregates and large honeycomb areas. For the casting of concrete into reinforced columns, long funnels are required that avoid disaggregation caused by drops of over one meter. First placing fine aggregate concrete slurry in the bottom of the column formwork reduces air pockets and assures adequate covering of the bars. Picture 19. Esmeraldas. Stirrups on cast columns and on prepared columns are spaced widely so they do not form the required caging of the concrete at the maximum moment areas. Omitting the closer spacing causes the broken concrete to fall out of the column and the column to fail. This lack of stirrups is one of the main causes of collapsing buildings, pan-caking and many human fatalities. Well designed reinforced concrete constructions in earthquake areas are characterized by closely spaced stirrups in all maximum moment areas of the columns and beams. When the earthquake forces exceed largely the design force (it is never known what will be the force of the earthquake!), the broken concrete will be contained in the cage and will still interact with the steel stress reinforcement. This will create a ductile and deforming connection that will absorb the impact of the shake and continue to withstand large forces without total structural collapse. Reinforced Concrete Construction Failures, May

10 The mass of the building is moved because of the earthquake. When the earthquake forces exceed the design parameters, the alternating forces of the earthquake first break the concrete on one side of the column and subsequently on the other side. By repeated movements and lack of stirrups, the broken concrete will fall out of the construction and the steel will bend, becoming useless. Picture 20. Esmeraldas. To allow large spans for the floors, these have been made stronger and stiffer by the use of hollow ceramic bricks and hollow cement blocks. The spaces between the blocks are filled with concrete to create T beams by which the top layer functions as the pressure layer. The sketch below is made from another photo. Like in the photo above it was observed that the large weight of the infill floor pulled the double reinforcement bars out of the narrow concrete T beams in between the infill blocks. The photo below was taken in a section of the building which was not yet build up to the second floor, showing the design of the floor with the hollow blocks. Replacing concrete by hollow bricks or cement blocks does bring the overall weight of the floor down as compared to a solid floor, but also adds on the dead weight of the hollow blocks. As can be observed from the picture above a lot of concrete will seep into the broken blocks, adding on mass. Using hollow cassette moulds or the very lightweight EPS (Expanded Polystyrene) is advised instead. Reinforced Concrete Construction Failures, May

11 Picture 21. Esmeraldas. Multi storey or apartment buildings tend to have slender columns using little floor space. In addition they require long floor spans, also minimizing the amount of columns. To minimise also the amount of beams, the floors are made with a high profile and therefore are becoming thick and stiff. In the upper line of sketches the building has thick and stiff floors with slender supporting columns. During a earthquake the bottom columns receive the largest forces and bend; walls crack and the whole building will pancake. In the second line of sketches the floors have a ductile design, allowing to absorb some of the shock. Floors will be waving and cracking. With properly designed columns the façade may crack, but the building would not collapse. Apartment buildings in which the floors are stiffer than the columns, and the columns do not have a ductile design, these buildings will collapse, pancake and cause the death of the inhabitants. Picture 22. Esmeraldas. A large building under construction had a design mistake in the upper floor dilatation joint. Due to the different horizontal movements of the two building blocks the line of supporting columns broke and the floor cracked. The sketch below shows the design mistake and a detail of the damaged column feet, also having inadequate amount of stirrups. Reinforced Concrete Construction Failures, May

12 Picture 23. Esmeraldas. The middle section of this building under construction collapsed because of a design mistake of a heavy awning or entrance overhang above the building main entrance. The vertical vibration of the earthquake broke the columns to which the awning is attached. Through failing of the two columns, the three floors above also collapsed. Several measurements would have avoided the above type of damage: (1) A much lighter construction, hence the earthquake force would have been much smaller. (2) Hanging the awning suspended from the floor above, not causing forces on the columns. (3) Having a couple of support columns under the outside of the awning. (4) Having made the two support columns deeper and stronger to withstand the additional load. (5) Having the awning individually supported, not being attached to the columns. Picture 24. Esmeraldas Staircases need to continue functioning as an escape route during an earthquake. Either the construction should be designed stronger or more ductile to withstand the earthquake forces. Diagonal forces may cause a horizontal load on the middle of a column, creating a moment force to which the column was not designed. Either the column should be reinforced here or the flight of the stairs loosely supported. Diagonal forces Damage on support columns Sliding supports Reinforced Concrete Construction Failures, May

13 3. MANAGUA, NICARAGUA On 23 December 1972 an earthquake magnitude 6.3 Richter struck the centre of the Managua, leaving over 5,000 death, over 20,000 injured and over 250,000 people homeless. All of the high rise buildings in Managua had reinforced concrete frame structures and although many were strongly damaged, only few of them totally collapsed and pancaked. As more often is the case, commercial high rise buildings are constructed according to adequate engineering standards, but lower buildings have less strict design standards applied to, and suffer less strict control during the building process. Engineers in Managua did not design according to the seismic requirements relative to the high earthquake risk if the area. Investigation by a team of engineers from the US National Bureau of Standards (NBS) and the National Academy of Engineering (NAE) performed field investigations 1. The team concluded that most damages appeared to result from the deficiencies in building practices, deficiencies which had been exhibited many times before in previous earthquakes, deficiencies which would have been avoided by implementation of up-to-date provisions for earthquake resistant design and construction. Picture 25. Managua (1980). Severe exterior non- structural damage in unbraced frame building Seguros La Protectora with typical scissor cracks. The force of an earthquake increases with the mass of the building. Therefore, with a equal column structure for all floors, the damage increases for every lower floor. Column reinforcement with a good caging of the maximum moment areas is most important at these lower floors. The reason for the area not being rebuilt lies largely in the political field, because the 1972 president Anastasio Somoza has stolen large part of the multi million dollar international humanitarian aid. Eventually these abuses of power led to the socialist Sandinista revolution, who toppled him and his government in July Secondly, lack of reconstruction lies in the economic field, because with the socialistic government no international investors were redeveloping their companies. By rebuilding permanent structures in the same area, the soil characteristics as well as the recent 1972 earthquake need to be taken into consideration. Because in 2010 the tectonic fault areas are better defined than 50 years ago, and more is known about soil structures, the building codes have a more precise zone definition for the risk level. However the government should have a proper regulatory system which is capable of the correct implementation of the building Codes before rebuilding. 1 NBS technical note TN-807. Building performance in the 1972 Managua Earthquake. 155 pages. Reinforced Concrete Construction Failures, May

14 4. ACEH, INDONESIA The earthquake of 26 December 2004 off the coast of Sumatra-Andaman had a magnitude of 9.2 Richter and resulted worldwide in over 230,000 deaths in fourteen countries, mainly due to the following tsunami. The position of the hypocentre was 160 km off the coast of Sumatra and at a depth of 30 km. Reconstruction activities took place over the next five years and included constructions that would better withstand earthquakes, especially in Indonesia. Although many reconstruction organisations had qualified staff and site supervision, not all project staff had the necessary knowledge to realise good quality earthquake resistant concrete work. For some the impression existed that a lot of reinforcement iron would make the building strong. However, it is more important that the iron is placed in the right places and concrete is good quality. Picture 26. Aceh. The amount of iron in the corner junction above the column does not allow concrete to work in unison with the steel. During an earthquake this junction will operate like a flexible hinge. The reinforcement design of the ring beams should be detailed showing the reinforcement bars going around the corner, instead of ending with hooks inside the columns. Left Sketch: Illustrates the applied reinforcement. In reality, four bars were applied in both the upper layer and bottom layer of the beam. Middle Sketch: Illustrates the correct application of the beam reinforcements. These go through the column, around the corner and end in a hook, providing minimal a 40 bar diameter overlap. The possibility exists to add another diagonal bar (dotted line) depending on the force calculations. In the areas of the maximum moment, in the beam as well as in the column, additional stirrups should have been placed with 5-6 cm spacing. Right Sketch: Illustrates the same principle for a T-junction. Reinforced Concrete Construction Failures, May

15 Picture 27. Aceh. Another picture from the same building complex. There is an absence of stirrups in the maximum moment area of the column. During an earthquake the short columns will most likely break just under the upper floor beam and above the lower foundation beam, possibly leading to the dropping of the building over 1.50 meter. The sketches below explain the process of failure during one forward and backward shock. In reality, a series of shocks occur during an earthquake, continuing the described process and resulting in the column collapsing, and with that bringing the building down. The following sketch on the left illustrates the forces that occur in the current structural design. Only the stilt column is subject to a strong bending moment, while the upper stiffener column and tie-beam only receive compression and stress forces when the infill masonry wall remains intact. In such a case, the steel bar reinforcement pattern sketched on the right is recommended. Better still is when the floor beam is lighter or thinner than the column, shifting the possible failure area to the beam. Reinforced Concrete Construction Failures, May

16 Picture 28. Aceh. Sand being collected from the seashore this should never be used for reinforced concrete. The high salt content of the sand will corrode the iron and the expanding iron will break off the outer layer of the concrete by which further corrosion will take place, especially in a seas side area. Picture 29. Aceh Smooth reinforcement bars have been pulled out of the broken concrete, demonstrating insufficient adherence to the concrete. This is often due to poor concrete quality, but sometimes can be caused by inappropriate steel design. More thin and profiled bars are recommended over a few large bars. Reinforced Concrete Construction Failures, May

17 5. BALAKOT, PAKISTAN The massive 7.6 Richter earthquake of 8 October 2005 destroyed all houses in Balakot, and caused heavy damage in Manshera and further districts of the Muzaffarabad region. The depth of this earthquake was about 25 km, its effects being spread over a 50 km wide area. In Islamabad, 65 km away, some poorly constructed apartment buildings, the Margalla towers, pancaked. Over 80,000 people were killed and over 3 million people were left homeless. The at that time estimated reconstruction cost was over 5000 million USD. Only about 250,000 of the approximate 780,000 damaged buildings were reinforced concrete constructions or combinations of reinforced concrete with masonry infill walls. Many of these houses collapsed and were damaged beyond repair due to lack of adherence to any earthquake building Code. Picture 30. Balakot. Column damage above the ground floor in a five storey building. Lack of closely spaced stirrups is shown here. The maximum moment in the column occurred just below the very stiff beam-floor construction. The whole building needs to be taken down because this damage cannot be repaired. With sufficient stirrups the situation may have been different, and with retrofitting, including some shear walls, the building could have been saved. Picture 31. Balakot. The lower part of a column. The poor quality of the concrete is visible here. Almost no large size stone aggregate and having a very porous structure. The lack of stirrups allowed the concrete crumbs to fall down. The steel bars come almost clean out of the broken concrete, indicating the inadequate adherence between the steel and the concrete. A low cement content, too much water, poor quality aggregates, or lack of vibration at the time of casting the columns do regularly occur with lack of adequate site supervision. When the quantity of the reinforcement bars is calculated on the lowest concrete quality ƒ b for reinforced columns of 21 N/mm 2 (210 kg/cm2), but this strength is not achieved, the construction will fail when moderately stressed. Reinforced Concrete Construction Failures, May

18 Picture 32. Balakot. Although this line of shops did not yet have their second stories, all of them were destroyed. Considering the extending reinforcement on the roofs, the addition of another storey was considered. Their connected length causes opposing wave forces in the same long building and part of the damage. The column design based on the lack of shear walls, should have been able to withstand the forces. Pictures. 33. Balakot. This building on the right had large concrete triangles as the upper part of the columns. When the thinner part of the columns failed (lack of stirrups) the triangles became the new legs under the roof. An example is in the left picture. The roof resting on the large triangles allowed the occupants to escape alive from the damaged building. It is unlikely that the building was designed to perform this way in case of earthquake failure, but it is possible to create safe areas in buildings using this design. Picture 34. Balakot. Pancaked building. Also the staircases totally collapsed reducing the possibility of escape. Iron reinforcement bars are being scavenged for reuse. Reinforced Concrete Construction Failures, May

19 Picture 35. Balakot. The generally poor concrete quality allowed the removal of the broken concrete from in between the reinforcement. For floor and roof reinforcements, the use of a thinner reinforcement mesh (welded) would have been more economic and would have provided better adherence to the concrete through the increased number of thinner bars RECONSTRUCTION. The reconstruction of Balakot required more than five years, is still ongoing and includes also the reconstruction of the stone masoned houses. To make the new houses more earthquake resistant the use of wall reinforcement and concrete columns will be an important part of the package. It was recognised by the Federal and Provincial State that training of village masons and contractors would be an essential element in the success of better reconstruction. This is especially so because most houses that will be reconstructed will be so called non-engineered constructions. In order to train large numbers of masons and concrete workers a cascade system of training was developed after a team of experts had developed appropriate curriculum on the subjects. 22 Training Coordinators were developed who became involved in: training at district level of 150 staff from Housing Reconstruction Centres was organised to become Master Trainers, who became involved in: training at council level of 650 staff from Partner Organisations to develop Mobile Teams. The Mobile Training Teams were in charge of the training of artisans, masons, self-builders, building contractors, communities, etc. An important task of these different training units was the awareness raising among the population about the possible seismic hazards and the reasons of the extensive building damage. Important in this phase was that it became better understood that earthquakes are recurrent natural phenomena, and that the resulting disasters were man-made due to poor construction habits. These trainings were realised in one-day programmes during which also the Earthquake Reconstruction and Rehabilitation Authority (ERRA) distributed guidelines and posters. In special programmes attention was given to educate the females because they often supervise house construction when the males are working elsewhere. Radio programmes included answering sessions of questions from the field. Newspapers focussed regularly on the issues and disseminated construction technology. Other media such as exhibitions and school discussions were part of the educational programmes that would lead to awareness raising among the population on better construction techniques. ************ Reinforced Concrete Construction Failures, May