In the mid-nineties, I was heading a civil style and design department for a huge EPC contractor in South East Asia. We experienced gained an purchase to construct a paper plant.
The most important setting up in a paper plant is the paper machine building. A usual paper machine building is about 300 m very long. The building usually has two flooring, a person at floor degree, and one at about 7.5 m level. The paper equipment is installed on a foundation that is not connected to the building. The equipment is obtainable from the device hall at 7.50 m degree. This constructing properties other intricate and weighty machinery and has incredibly stringent prerequisites with respect to high quality, structural design and style and balance. The roof is substantial up and some of the sections of this setting up are matter to temperatures amongst 50 to 60 C. A significant overhead crane straddles the upstairs equipment corridor. The differential settlement in the paper machine basis has to be less than 1 mm and all round settlement at any issue a lot less than 1.25 mm. This developing, with all its parts and the equipment foundations, commonly requires 18 months to make.
Our taking care of director was an revolutionary male and continually sought ideas to speed up construction. A person working day, he named me to his workplace and confirmed me an write-up narrating about a firm in the US that had designed approaches to make a paper machine setting up utilizing pre cast factors. This paper device setting up was finished in a history time of 6 months, stated the report. We appointed the US organization as our consultants and they did the engineering with the help of our engineers in our business. We crafted our paper equipment building in a yr chopping down the time by about six months. This was inspite of a hold off of about 3 months due to the finding out curve and the time required for setting up a precast plant.
Consequently commenced my 20 two a long time long affiliation with pre-forged concrete. My outdated corporation has designed various massive industrial vegetation and other buildings because then.
In numerous first planet nations around the world pre solid aspects for bridges, culverts have been standardized. Pre-casting units are positioned in the vicinity of significant metropolitan areas that offer these features to the building web sites. This not only lowers the design time but also the design time as one uses normal aspects whose qualities are recognized.
There are variations of the precast concrete building these as tilt up development, module fitments etc.
I have often puzzled why India, with so considerably design necessary in the all the sectors of building, has not embraced this system. Aside from other concerns like have to have for repetition, unfriendly taxation, requirement of transportation or lifting machinery and so forth., I imagine our engineers have not offered a severe thought to developing this approach.
I would like to share some of my learnings.
1. Scheduling is Paramount: The construction to be built from precast things has to be damaged down in factors, in a pre-established configuration. It is like creating the parts of a jigsaw puzzle that when place with each other will kind the done puzzle. It can be a mix of typical and non-common items.
2. God is in details: Every element as a result prepared has to be in-depth out to in good shape all the factors on all its sides and the embedment required for utilities.
3. Design and style the Design and Assemble the design: Regular structural engineering apply of designing the ultimate product and leaving the “How?” to the construction staff, does not get the job done in precast. The structural engineer has to keep included in the approach of pre casting, erection and placement.
To the most effective of my know-how, IS codes do not have distinct provisions for pre cast structures unlike ACI or BS codes. Some of the clauses in ACI can be substituted by provisions in their supplementary publications. These kinds of provisions have to be applied judiciously soon after a right assessment of the stages in the services life of the element. A foremost pro on pre-casting when stated “Implementing provisions of R.C.C code to pre-casting would be like enjoying tennis with a baseball bat”
The structural design and style for a precast factor is completed for numerous phases of in its early existence. Several level checks are demanded until the ingredient is placed, far more checks are demanded if it is a pre-pressured component with partial un-bonding of tendons.
4. Joints can trigger headaches: Resolving and configuring a joint between precast things can be an arduous task. It will become a heuristic system to balance involving the structural necessity, functionality with regard to standard consideration as drinking water tightness, and the sizing of the components to which an component in thing to consider is attached. Joints have to be made the way they have been envisaged.
5. Chopping off ears mainly because they stick out, not only impairs hearing but also produces trouble in donning spectacles: This is acknowledged to happen often wherever architectural prerequisites are of most important value. Ordinarily some architects do not like some critical arrangements made for much better joints. Doing absent with these “hindering” aspects may perhaps guide to diminished performance of the joints or the things. Expensive alternate arrangements are essential to restore functionality.
6. Design Methodology can make or split a project: Many decades ago, a huge bulk warehouse with pre-forged pre stressed concrete bow string girders as roof trusses was remaining made in India for a fertilizer plant. Out of twelve bowstring girders, 6 broke even though being lifted though the other people were being erected effortlessly. Patterns had been checked and double checked and checked all over again. This was right before the easy availability of the subtle finite component evaluation that we have these days. It finally dawned on somebody that the bow string girders broke because a girder though getting lifted in tandem by two cranes, twisted out of aircraft due to various prices of lifting. A structural engineer planning precast elements really should, thus, have the expertise of the lifting procedure.
7. High-quality is the watchword: Steady High-quality of output is a person of the arguments place ahead by the advocates of precast. But a lot of a mismatches, rejections and failures have occurred owing to seeing only the high-quality of concrete and offering less relevance to placement of reinforcement embeds and the dimensional tolerances.
8. A just one rupee improve in the manufacturing expense can indicate a crore of rupees at the stop: Due the repetitive character of the charge of pre-casting a great deal of imagined has to be offered to use any “pleasant to have” component. Even though the most apparent price features associated to concrete are watched vigilantly, a small embed or a depth, that is included in the style and design and casting of an component for a possible use, escapes notice. These types of an embed that was proposed to be employed and has been cast in the aspect has currently added to the value of developing the aspect. When a quantity of these components are solid, the expenditure can be considerable. If these kinds of redundancy if not eradicated in time, it can squander lakhs of rupees.