Posts Tagged ‘Construction’

Precast Concrete Construction

May 15th, 2021

In the mid-nineties, I was heading a civil design department for a large EPC contractor in South East Asia. We had received an order to build a paper plant.

The primary building in a paper plant is the paper machine building. A typical paper machine building is about 300 m long. The building typically has two floors, one at ground level, and one at about 7.5 m level. The paper machine is installed on a foundation that is not connected to the building. The machine is accessible from the machine hall at 7.50 m level. This building houses other complex and heavy machinery and has very stringent requirements with respect to quality, structural design and stability. The roof is high up and some of the sections of this building are subject to temperatures between 50 to 60 0 C. A large overhead crane straddles the upstairs machine hall. The differential settlement in the paper machine foundation has to be less than one mm and overall settlement at any point less than 1.25 mm. This building, with all its components and the equipment foundations, normally takes 18 months to build.

Our managing director was an innovative man and constantly sought ideas to speed up construction. One day, he called me to his office and showed me an article narrating about a company in the US that had developed techniques to build a paper machine building using pre cast elements. This paper machine building was completed in a record time of 6 months, said the article. We appointed the US company as our consultants and they did the engineering with the help of our engineers in our office. We built our paper machine building in a year cutting down the time by about six months. This was despite a delay of about three months due to the learning curve and the time required for setting up a precast plant.

Thus began my twenty two years long association with pre-cast concrete. My old company has built several large industrial plants and other structures since then.

In many first world countries pre cast elements for bridges, culverts have been standardized. Pre-casting units are located near major cities that supply these elements to the construction sites. This not only reduces the construction time but also the design time as one uses standard elements whose properties are known.

There are variations of the precast concrete construction such as tilt up construction, module fitments etc.

I have often wondered why India, with so much construction needed in the all the sectors of construction, has not embraced this technique. Apart from other issues like need for repetition, unfriendly taxation, requirement of transport or lifting machinery etc., I think our engineers have not given a serious thought to developing this technique.

I would like to share some of my learnings.

1. Planning is Paramount: The structure to be built from precast elements has to be broken down in elements, in a pre-determined configuration. It is like making the pieces of a jigsaw puzzle that when put together will form the completed puzzle. It can be a combination of standard and non-standard pieces.

2. God is in details: Each element thus planned has to be detailed out to fit all the elements on all its sides and the embedment required for utilities.

3. Design the Construction and Construct the design: Normal structural engineering practice of designing the final product and leaving the “How?” to the construction personnel, does not work in precast. The structural engineer has to stay involved in the process of pre casting, erection and placement.

To the best of my knowledge, IS codes do not have specific 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. Such provisions have to be applied judiciously after a proper assessment of the stages in the service life of the element. A foremost expert on pre-casting once said “Applying provisions of R.C.C code to pre-casting would be like playing tennis with a baseball bat”

The structural design for a precast element is done for various stages of in its early life. Multiple level checks are required till the element is placed, more checks are required if it is a pre-stressed element with partial un-bonding of tendons.

4. Joints can cause headaches: Resolving and configuring a joint between precast elements can be an arduous task. It becomes a heuristic process to balance between the structural requirement, functionality with respect to basic consideration as water tightness, and the size of the elements to which an element in consideration is attached. Joints have to be constructed the way they have been envisaged.

5. Cutting off ears because they stick out, not only impairs hearing but also creates difficulty in wearing spectacles: This is known to occur frequently where architectural requirements are of primary importance. Typically some architects do not like some essential arrangements created for better joints. Doing away with these “hindering” details may lead to reduced functionality of the joints or the elements. Expensive alternate arrangements are required to restore functionality.

6. Construction Methodology can make or break a project: Many years ago, a large bulk warehouse with pre-cast pre stressed concrete bow string girders as roof trusses was being constructed in India for a fertilizer plant. Out of twelve bowstring girders, six broke while being lifted while the others were erected smoothly. Designs were checked and double checked and checked again. This was before the easy availability of the sophisticated finite element analysis that we have today. It finally dawned on someone that the bow string girders broke because a girder while being lifted in tandem by two cranes, twisted out of plane due to different rates of lifting. A structural engineer designing precast elements should, therefore, have the knowledge of the lifting process.

7. Quality is the watchword: Consistent Quality of production is one of the arguments put forward by the advocates of precast. But many a mismatches, rejections and failures have occurred due to watching only the quality of concrete and giving less importance to placement of reinforcement embeds and the dimensional tolerances.

8. A one rupee increase in the production cost can mean a crore of rupees at the end: Due the repetitive nature of the cost of pre-casting a lot of thought has to be given to use any “nice to have” component. While the most obvious cost elements related to concrete are watched vigilantly, a small embed or a detail, that is incorporated in the design and casting of an element for a probable use, escapes attention. Such an embed that was proposed to be used and has been cast in the element has already added to the cost of producing the element. When a number of such elements are cast, the expenditure can be substantial. If such redundancy if not eliminated in time, it can waste lakhs of rupees.

GEM believes in providing an open work culture in which employees get opportunities to hone their skills, thrive in a professional environment and develop an entrepreneurial mind-set. Our goal is to provide value added technical service of International Quality at competitive price. We believe in a continual update of skills of our employees and client’s engineers and these blogs are aimed at achieving this objective.

7 Ways Construction Firms Can Hire and Retain Quality Tradesmen

February 15th, 2021

Whether you are a construction recruitment agency or a construction firm itself looking to hire the best of talent industry has to offer, here are a few important tips to help you in this quest.

Hire in the off season:

Conventional wisdom has it that you must never go grocery shopping while you are hungry. You tend to buy whatever you get at the earliest and that’s almost never a good bargain. The same is true for hiring tradesmen when you need them.

So the best time to look for a tradesman is when you don’t require one. It will help you scan wide range of talents, be more selective, and acquire the kind of worker you exactly want. As an added piece of advice, aim for the off-season when many construction workers are out of work and you might get a bargain.

Pay the market rate:

When you pay peanuts, you get only monkey! Firms who pay below-market wages not only have the least-qualified and least-productive employees, but they are also the ones always in need of new workers. Why? Because competitive tradesmen will leave you the moment they get more lucrative opportunities. Do I need to tell you what a dent it makes to overall productivity?

Provide a safe work environment:

Don’t underestimate the value of a safe and healthy workplace in retaining workforce. Too many workers falling sick on site might force others to look for a safer option. A major accident on site and the resultant bad press might turn away potential hires.

Develop a great work culture:

There is something more than a good salary a qualified and talented tradesman look forward to. Bonuses, paid leaves, company outings, work-life balance, and retirement programs are some of the perks that entice the best of talents. The more people want to work for your company, the easier it will be to attract (and retain) quality people.

Invest in your workforce:

I haven’t met a tradesman who doesn’t like adding on new skills or getting a pat on the back for a job well done. So it’s a good idea to invest in your workforce. When you provide them a chance to learn, grow and develop they can help your company do the same. Training improves the efficiency of the workers and quality of the output. This is also a great way to identify the people with potential to take on bigger roles within the company.

Be in step with time and technology:

Embracing technology not only makes the company more efficient and productive but it also attracts younger and tech-savvy workforce. You can also publicize it as your USP to entice people buying your product or services.

Character can pay more dividend than the skill-set of a hire:

Characters can’t be built, skills can be. People with character can make the most of the training you give them. Such workers are more likely to stick with you in bad times as compared to those with only skills and potential.