In the mid-nineties, I was heading a civil style office for a big EPC contractor in South East Asia. We had obtained an buy to create a paper plant.
The most important creating in a paper plant is the paper equipment building. A typical paper device building is about 300 m very long. The constructing usually has two flooring, just one at ground level, and one particular at about 7.5 m stage. The paper device is set up on a foundation that is not related to the developing. The machine is accessible from the device corridor at 7.50 m level. This constructing properties other complex and weighty equipment and has really stringent prerequisites with regard to quality, structural style and balance. The roof is high up and some of the sections of this building are issue to temperatures among 50 to 60 C. A substantial overhead crane straddles the upstairs machine corridor. The differential settlement in the paper equipment basis has to be less than one particular mm and overall settlement at any point fewer than 1.25 mm. This making, with all its factors and the equipment foundations, usually normally takes 18 months to build.
Our taking care of director was an impressive guy and continually sought strategies to speed up development. A single day, he called me to his business office and showed me an short article narrating about a firm in the US that had designed approaches to establish a paper machine building applying pre solid elements. This paper machine making was finished in a file time of 6 months, stated the post. We appointed the US business as our consultants and they did the engineering with the help of our engineers in our office environment. We constructed our paper machine setting up in a calendar year reducing down the time by about 6 months. This was irrespective of a delay of about 3 months owing to the discovering curve and the time required for environment up a precast plant.
Hence began my 20 two many years extended affiliation with pre-cast concrete. My outdated corporation has created numerous large industrial vegetation and other constructions since then.
In numerous to start with world nations around the world pre cast features for bridges, culverts have been standardized. Pre-casting models are positioned in close proximity to main towns that provide these components to the construction web pages. This not only reduces the building time but also the layout time as just one makes use of common components whose properties are regarded.
There are variations of the precast concrete development these as tilt up design, module fitments and so on.
I have generally questioned why India, with so considerably building desired in the all the sectors of design, has not embraced this strategy. Aside from other issues like will need for repetition, unfriendly taxation, prerequisite of transportation or lifting machinery etc., I assume our engineers have not presented a critical considered to developing this approach.
I would like to share some of my learnings.
1. Planning is Paramount: The construction to be constructed from precast features has to be broken down in components, in a pre-identified configuration. It is like producing the pieces of a jigsaw puzzle that when put together will type the done puzzle. It can be a mixture of typical and non-conventional pieces.
2. God is in particulars: Each and every ingredient hence planned has to be detailed out to healthy all the things on all its sides and the embedment expected for utilities.
3. Design the Construction and Construct the design: Typical structural engineering follow of developing the final product or service and leaving the “How?” to the development personnel, does not get the job done in precast. The structural engineer has to remain included in the course of action of pre casting, erection and placement.
To the most effective of my information, IS codes do not have precise provisions for pre forged constructions unlike ACI or BS codes. Some of the clauses in ACI can be substituted by provisions in their supplementary publications. This kind of provisions have to be used judiciously right after a correct evaluation of the stages in the assistance life of the component. A foremost expert on pre-casting at the time stated “Applying provisions of R.C.C code to pre-casting would be like taking part in tennis with a baseball bat”
The structural design for a precast aspect is finished for several phases of in its early everyday living. A number of stage checks are needed till the ingredient is put, much more checks are expected if it is a pre-stressed aspect with partial un-bonding of tendons.
4. Joints can induce complications: Resolving and configuring a joint involving precast components can be an arduous activity. It gets to be a heuristic process to balance in between the structural prerequisite, functionality with regard to standard thought as h2o tightness, and the sizing of the aspects to which an ingredient in consideration is connected. Joints have to be manufactured the way they have been envisaged.
5. Chopping off ears because they stick out, not only impairs listening to but also produces difficulty in wearing spectacles: This is recognised to occur routinely in which architectural specifications are of most important value. Generally some architects do not like some important preparations established for far better joints. Doing away with these “hindering” aspects could guide to diminished performance of the joints or the components. High priced alternate arrangements are expected to restore operation.
6. Development Methodology can make or crack a challenge: Lots of a long time back, a big bulk warehouse with pre-cast pre pressured concrete bow string girders as roof trusses was staying built in India for a fertilizer plant. Out of twelve bowstring girders, 6 broke when currently being lifted whilst the many others were being erected smoothly. Types ended up checked and double checked and checked all over again. This was right before the uncomplicated availability of the complex finite element evaluation that we have currently. It finally dawned on an individual that the bow string girders broke since a girder although being lifted in tandem by two cranes, twisted out of plane thanks to unique fees of lifting. A structural engineer coming up with precast things should, hence, have the knowledge of the lifting process.
7. Good quality is the watchword: Reliable Top quality of generation is just one of the arguments set forward by the advocates of precast. But many a mismatches, rejections and failures have happened because of to seeing only the top quality of concrete and giving less worth to placement of reinforcement embeds and the dimensional tolerances.
8. A just one rupee enhance in the manufacturing price can indicate a crore of rupees at the finish: Because of the repetitive character of the charge of pre-casting a whole lot of imagined has to be offered to use any “pleasant to have” part. Although the most apparent price factors similar to concrete are viewed vigilantly, a little embed or a element, that is integrated in the style and design and casting of an component for a probable use, escapes attention. These types of an embed that was proposed to be utilised and has been solid in the factor has by now extra to the expense of generating the element. When a amount of such things are forged, the expenditure can be significant. If these types of redundancy if not removed in time, it can squander lakhs of rupees.