In the mid-nineties, I was heading a civil style and design department for a large EPC contractor in South East Asia. We experienced acquired an buy to construct a paper plant.
The main constructing in a paper plant is the paper equipment creating. A common paper equipment constructing is about 300 m prolonged. The creating ordinarily has two floors, a single at ground degree, and one at about 7.5 m degree. The paper device is put in on a foundation that is not linked to the developing. The machine is available from the device corridor at 7.50 m stage. This building homes other intricate and heavy equipment and has extremely stringent requirements with regard to high quality, structural style and security. The roof is superior up and some of the sections of this setting up are topic to temperatures concerning 50 to 60 C. A significant overhead crane straddles the upstairs device hall. The differential settlement in the paper machine basis has to be significantly less than one mm and general settlement at any place less than 1.25 mm. This creating, with all its elements and the devices foundations, typically can take 18 months to develop.
Our handling director was an ground breaking guy and constantly sought concepts to speed up building. A single day, he named me to his office and confirmed me an posting narrating about a corporation in the US that experienced made methods to construct a paper machine creating making use of pre cast features. This paper device creating was finished in a report time of 6 months, mentioned the report. We appointed the US company as our consultants and they did the engineering with the assist of our engineers in our business. We crafted our paper machine making in a calendar year reducing down the time by about 6 months. This was despite a hold off of about three months because of to the studying curve and the time expected for environment up a precast plant.
Therefore began my 20 two several years long affiliation with pre-forged concrete. My previous corporation has constructed numerous substantial industrial crops and other structures due to the fact then.
In several very first world international locations pre forged aspects for bridges, culverts have been standardized. Pre-casting units are situated in the vicinity of major towns that offer these things to the construction web-sites. This not only lessens the design time but also the style time as just one works by using regular things whose qualities are recognized.
There are variants of the precast concrete building these kinds of as tilt up construction, module fitments etcetera.
I have frequently wondered why India, with so considerably construction essential in the all the sectors of design, has not embraced this strategy. Aside from other problems like want for repetition, unfriendly taxation, prerequisite of transport or lifting machinery etc., I consider our engineers have not presented a serious assumed to developing this system.
I would like to share some of my learnings.
1. Organizing is Paramount: The construction to be created from precast elements has to be broken down in things, in a pre-established configuration. It is like producing the pieces of a jigsaw puzzle that when put with each other will type the done puzzle. It can be a blend of typical and non-typical items.
2. God is in information: Each element as a result planned has to be comprehensive out to fit all the components on all its sides and the embedment needed for utilities.
3. Layout the Building and Assemble the style and design: Typical structural engineering follow of creating the remaining solution and leaving the “How?” to the design staff, does not do the job in precast. The structural engineer has to remain associated in the approach of pre casting, erection and placement.
To the very best of my information, IS codes do not have precise provisions for pre forged buildings unlike ACI or BS codes. Some of the clauses in ACI can be substituted by provisions in their supplementary publications. These types of provisions have to be utilized judiciously immediately after a right assessment of the levels in the support daily life of the component. A foremost expert on pre-casting once stated “Making use of provisions of R.C.C code to pre-casting would be like taking part in tennis with a baseball bat”
The structural structure for a precast component is accomplished for many phases of in its early life. Multiple amount checks are demanded till the aspect is put, extra checks are necessary if it is a pre-stressed component with partial un-bonding of tendons.
4. Joints can result in head aches: Resolving and configuring a joint concerning precast elements can be an arduous job. It gets to be a heuristic course of action to balance in between the structural need, features with regard to basic thought as h2o tightness, and the measurement of the elements to which an aspect in consideration is connected. Joints have to be created the way they have been envisaged.
5. Slicing off ears for the reason that they adhere out, not only impairs hearing but also results in issues in putting on spectacles: This is acknowledged to manifest often the place architectural prerequisites are of most important significance. Generally some architects do not like some important preparations developed for greater joints. Carrying out away with these “hindering” specifics might guide to decreased performance of the joints or the elements. High priced alternate preparations are expected to restore features.
6. Building Methodology can make or crack a challenge: Quite a few a long time back, a big bulk warehouse with pre-forged pre pressured concrete bow string girders as roof trusses was currently being created in India for a fertilizer plant. Out of twelve bowstring girders, six broke though being lifted while the other folks were erected effortlessly. Models were being checked and double checked and checked once again. This was prior to the easy availability of the advanced finite factor examination that we have now. It finally dawned on anyone that the bow string girders broke since a girder whilst remaining lifted in tandem by two cranes, twisted out of plane because of to diverse rates of lifting. A structural engineer building precast elements ought to, hence, have the know-how of the lifting procedure.
7. Excellent is the watchword: Constant High quality of output is 1 of the arguments put forward by the advocates of precast. But quite a few a mismatches, rejections and failures have transpired because of to watching only the high quality of concrete and providing a lot less great importance to placement of reinforcement embeds and the dimensional tolerances.
8. A 1 rupee increase in the creation price can imply a crore of rupees at the stop: Due the repetitive character of the cost of pre-casting a whole lot of considered has to be supplied to use any “good to have” ingredient. Even though the most noticeable cost things associated to concrete are viewed vigilantly, a smaller embed or a detail, that is incorporated in the style and casting of an component for a probable use, escapes notice. These kinds of an embed that was proposed to be made use of and has been solid in the factor has already added to the cost of making the factor. When a selection of this sort of things are cast, the expenditure can be significant. If this sort of redundancy if not eliminated in time, it can squander lakhs of rupees.
