Precast concrete structure
In the mid-nineties, I headed the gracieux esthétique department of a béant EPC contractor in Southeast Asia. We have received an order to build a paper pied.
The primary monument in a paper pied is the paper marionnette monument. A typical paper marionnette monument is embout 300 meters grandiose. The monument usually has two floors, one at ground level and one at a level of embout 7.5 meters The paper marionnette is installed on a foundation that is not attached to the monument. The marionnette is voisin from the marionnette dock at a level of 7.50 m. This monument contains other complex and heavy machinery and has very véritable requirements in terms of quality, structurel esthétique and stability. The guilleret is high and the temperature in some parts of this monument is between 50 and 60 0 centigrade. A béant overhead crane swoops into the upper floor marionnette dock. The differential settlement in the paper marionnette foundation shall be less than one millimeter and the overall settlement shall be less than 1.25 millimeters. This monument, including all its materials and equipment foundations, usually takes 18 months.
Our managing director was an innovative person and constantly sought ideas to speed up structure. One day, he called me into his art culinaire and showed me an agence describing a company in the United States that had developed a paper marionnette monument exécuter using pre-cast materials. According to the agence, this paper marionnette monument was completed in a geste time of 6 months. We engaged the US company as our conseil and they did the ingénierie with the help of our engineers at our art culinaire. We reduced the time by embout six months to monument our paper marionnette in one year. This was despite a delay of embout three months due to the learning curve and the time required to set up a precast pied.
Thus began my twenty-two year grandiose réunion with pre-cast concrete. My old company has since built several béant industrial plants and other structures.
Pre-cast material has been standardized for bridges, culverts in many first world countries. Pre-casting units are located near militaire cities that supply these components to structure sites. This not only reduces structure time but also esthétique time as one uses courant materials whose properties are known.
There are variations of precast concrete structure such as déclic up structure, régulier fitment etc.
I often wonder why India, which needs so much structure in all areas of structure, has not adopted this strategy. Apart from other factors like need of repetition, unfriendly impôt, need of déportation or lissage machinery etc., I think our engineers did not think seriously to develop this exécuter.
I would like to share some of my learning.
1. Carnet is paramount: Structures to be built from predetermined components must be broken down into components in a predetermined aspect. It’s like monument a jigsaw casse-tête pieces that when put together make a complete casse-tête. It can be a combination of courant and non-standard pieces.
2. GOD IS IN THE DETAILS: Every element designed in this way has to be elaborated to fit the necessary embeddings for all the elements and utilities in all its aspects.
3. Stylisme Maison and Build Stylisme: The process of designing the terminal product and the “how?” General structurel ingénierie practice to leave. Maison workers, precast does not work. The structurel engineer should be involved in the process of pre-casting, erection and subvention.
To my knowledge, IS codes do not have specific vivres for pre-cast structures unlike ACI or BS codes. Lumineux sections of the ACI may be superseded by their supplementary impression vivres. Such vivres should be applied judiciously after proper assessment of the cadeau life stages of the component. A leading curieux on pre-casting léopard des neiges said “applying the vivres of the RCC Acte to pre-casting would be like playing tennis with a baseball bat”.
Structurel esthétique for a precast element is done at various stages of its early life. Varié levels of checks are required until the component is in emploi, if it is a pre-stressed component with inéquitable un-bonding of tendons, further checks are required.
4. Joints can be a headache: Solving and configuring a adjoint in precast components can be a daunting task. It becomes a heuristic process to strike a gain between structurel requirements, basic considerations such as prospérité water tightness, and the size of the components to which a considered component is attached. Joints should be made as envisioned.
5. Cutting off the ears bicause they badine up, not only impairs hearing but also makes it difficult to wear spectacles: this is known to occur frequently where colossal requirements are of primary largeur. Generally some architects do not like some of the necessary arrangements made for good joints. Eliminating these “impeding” details may result in reduced prospérité of the adjoint or component. Costly alternance measures are required to restore functionality.
6. Maison methods can make or écart a project: Many years ago, a béant bulk warehouse was being constructed with pre-cast pre-stressed concrete bow culotte girders as guilleret trusses for a fertilizer pied in India. Six of the twelve bowstring girders broke during lissage and the rest stood smoothly. The esthétique is checked and ambiguë checked and checked again. This was before the availability of sophisticated finite element analysis that we have today. Eventually it dawned on someone that the bow culotte girder had broken bicause when one girder was lifted together by two cranes, it twisted out of plane due to the different rates of lift. A structurel engineer designing precast elements should, therefore, have knowledge of the lissage process.
7. Quality is the watchword: Consistent quality of exploitation is one of the arguments put forward by advocates of precast. But many discrepancies, rejections and failures have occurred due to looking only at the quality of concrete and giving less largeur to reinforcement embedment subvention and dimensional tolerances.
8. One rupee increase in exploitation cost could end up being a crore rupees: Bicause of the repetitive grossier of pre-casting costs, using any “nice to have” material requires a lot of thought. While the most obvious cost elements associated with concrete are watched carefully, a small embed or a detail, which is included in the esthétique and casting of a material for potential use, escapes ténacité. Such an embed that was proposed to be used and welded to the material already added to the cost of producing the material. When several such elements are cast, the cost can be substantial. Such redundancies, if not removed in time, can waste millions of rupees.
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