One example of a durability issue in predominantly concrete structures is that of the manner of loading of concrete (Moehle and Mahin, 1998). The concept of concrete structures involves the continuous loading of the material in order to establish enough strength that could survive any disturbances within the structure. Continuous loading also ensures durability of the concrete from the foundation, to the upper regions of the structure.
Any insufficiency or failure to perform continuous loading of concrete may result in the collapse of the structure, especially when earthquakes and any strong forces influence the building. Durability of predominantly concrete structures provides ample reinforcement to engineering materials, as these are generally erected as vertical components of a bigger structure, such as a building. It may be possible that discontinuity of loading of concrete was performed when shear walls were designed to be part of the structure.
This is often observed in the upper floors of buildings that are made of more than 2 stories. In this situation, the first floor is generally made of soft materials and thus any forces that suddenly occur, such as those from earthquakes, can result in a concentrated and accumulated form of damage that often results in the destruction of the lower floor. Another example of a durability issue with predominantly concrete structures is seepage of water (ODNR, 1999). This occurrence generally occurs underneath concrete spillways, as well as headwalls.
Seepage also often occurs when a building is not equipped with a weep hole, or other provisions such as relief drains, which mainly serve as relievers of pressure generated by the presence of water. It should be understood that the coupled processes of freezing, then thawing, increases the likelihood of water seepage. It is also possible that surface water could infiltrate the concrete structure. The water level of lakes can also increase the likelihood of water seepage through concrete structures. (b) Two examples where durability has been an issue for a predominantly steel structure
Durability is an issue for a predominantly steel structure when cracks develop at the borders of these structural materials. It has recently been reported by Popelukh et al. (2008) steel structures can develop cracks when these are exposed to conditions of dynamic compression. The cracks gradually undergo chipping, which in turn increases the chances of developing a wedging effect. Through time, the sites of chipping serve as the main points were destruction of the structure takes place. Dynamic compression is considered as a type of loading which can influence the formation of a crack.
Aside from steel structures, cracks can also occur in plastic materials. The most common scenario for a crack to develop in steel structures involves the development of a band that is positioned 45 degrees in relation to the source of the force. Microcracks initially develop, which then propagate in a planar fashion to the source of the force, resulting in a bigger shear. Through time, a single main crack can be observed in the steel structure. In order to prevent development of cracks, it is important to include support structures between steel components so that the effect of compression would be decreased.
Deformation of steel structures can also pose problems in durability (Keras and Mockiene, 2007). Deformation of steel structures pertains to the failure of this material to serve as a stable and solid entity in buildings. It should be understood that the process of deformation is closely associated with the development of cracks in steel structures. Deformation influences the degree of durability of steel structures, especially when there is an overloading of weight or pressure on the structure.
Previously accumulated deformations can decrease the durability of the structure and the continuous loading of pressure can further deform the material. In addition, the steel structure can be more vulnerable to the next episode of overloading, possibly resulting in the total collapse of the steel structure at any future point in time. Deformation of steel structures can also be caused by pollution, as well as exposure to corrosive chemicals. In order to prevent deformation of steel structures, these materials should be well insulated from corrosive materials.
In addition, steel components should also be intermittently insulated with concrete or other sturdy materials to decrease the effect of weight or pressure. 2. An interesting innovation in the field of engineering is the use of tilt-up construction, which presents a number of advantages over the employment of steel or concrete (Alcon and Associates, 2009). Aside from the lower net cost of construction of buildings, the tilt-up method uses locally manufactured concrete raw materials which do not have to be shipped over lengthy distances.
This mode of construction also involves the erection of panels and thus may be completed at a shorter time than creating concrete walls. These walls are generally durability because these are mixed with concrete. Based on the history of use of tilt-up construction, this type of engineered facilities are stable because these are mainly based on the ground, instead of using scaffolds, which increases the likelihood of overloading and pressure of the structural materials. The first tilt-up concrete edifices were erected in the 1940’s and are still operational to this date.
In addition, the state of California, which is most frequently affected by earthquakes, currently uses this type of construction for approximately 90% of its industrial buildings. Tilt-up construction projects are also found to be durable because it allows isolation of fire to a specific region of the building and the walls are impervious to heat. This resistance can prevent the further spread of fire which could deform steel structures in predominantly steel buildings.
The main principle behind tilt-up construction is the use of panels that are mixed with concrete to generate a sturdy construct that is both durable and fire-resistant. It is thus a common occurrence that predominantly steel buildings have to be meticulously checked for fire hazards because steel is easily deformed and destroyed by fire and heat.
Alcon and Associates. (2009). Tilt-up concrete construction vs. steel. Downloaded from http://www. alconconstruction. com/tilt-up-construction-vs-steel.php on May 26, 2009. Keras, V. and Mockiene, J. (2007). On the precritical destruction of metal (steel) structures. Dowloaded from http://www. vgtu. lt/leidiniai/leidykla/MBM_2007/3pdf/Keras_Mockiene. pdf on May 26, 2009. Moehle, J. P. and Mahin, S. A. (1998). Observations on the behavior of reinforced concrete buildings during earthquakes. National Information Service for Earthquake Engineering, University of California, Berkeley. Downloaded from http://nisee. berkeley. edu/lessons/concretemm.
html on May 25, 2009. Ohio Department of Natural Resources (1999). Dam safety: Seepage through earthen dams. Fact Sheet 94–31. Downloaded from http://www. dnr. state. oh. us/Portals/7/pubs/pdfs/fctsht31. pdf on May 25, 2009. Popelukh A. I. , Bataev V. A. and Ivanchenko, V. A. (2008). Features of structure influence on the mechanism of steel destruction at repeated dynamic load under compression scheme. Downloaded from http://ieeexplore. ieee. org/stamp/stamp. jsp? arnumber=04602899 on May 26, 2009.
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