Concrete Prefabrication
Reinforced concrete has turned out to rule as number one building material since more than a century. Its structural strength, its durability, its versatility allow for a unique range of usage. Its usage comprises a really building parts like slabs and walls as well as rod-like structurally effective – members like line foundations, columns, beams, and purlins.
The logistic task of producing concrete elements and members is quite challenging. One needs scaffolding, formwork, steel in various shapes and the ingredients of course, mainly sand, water, and cement– together with a reasonably educated labor force and the unavoidable planning.
Even though there is no feasible alternative to reinforced concrete at our disposal. Thus we would need to consider the optimization of the building process with concrete.
Execution On-site
The limitations of on-site execution are more than obvious: all necessary materials and labor need to be moved to the building site, all steps of execution are to be performed in place. There is only so much which can be done in one step of execution. That includes the setup of the formwork, the preparation and placement of reinforcement and built-in parts and the procurement and pouring of the concrete. All works and trades are done once and can be reused to a minor extent only.
Thus execution of on-site concrete parts tends to be slow and inefficient. The exposition to wind and weather often in perilous altitudes does not encourage for quality and quality control. The need of concreting upright members in-situ and the limitation of what can be mixed in place cause many casting segments thus leading to ugly seams and increase of the structural risks.
Factory Production
The production of concrete elements in factories provides an abundance of advantages which come with the setup of stationary processes: All tools and materials are easily available and can be maintained and provided in a continuous, well established process. Skilled workforce can settle down close to their daily working area. Working in shifts may contribute to a higher exploitation of the investments undertaken.
The conditioned environment allows for optimal procedures and continuous quality control including the requisite documentation of each and every production step. Higher concrete grades improve the structural rigidity and shorten the curing process.
All members can be done in horizontal formwork. Formwork – preferably in steel – which can be used many a times, even for years, providing a smooth and seamless surface and a precision which is simply not achievable on site.
Pre-stressed trusses can bridge over 30 meters and have become quite popular with the investors in logistic buildings where any columns are obstacles to the workflow only.
Transport and Assembly On-site
Concrete members tend to be heavy. The removal out of the formwork and the handling in the factory require powerful and reasonably fast moving cranes.
There is a limit to the maximum size and weight of parts which can be brought to site and assembled over there. It is advantageous on the other hand to reduce the number of elements thus saving assembly steps and joints and providing the desired column-free handling areas.
These dimensions depend on the available infrastructure and traffic regulations. Wall and slabs of up to 4 m height, lengths of 10 m and thicknesses up to 25 cm are common in Central Europe. Columns of a 20 m length and more come with their complete foundation in one piece. Considering the recent and remarkable improvement in India’s infrastructure comparable dimensions should be in range of feasibility.
The assembly requires precise survey and installation. The tolerances are less than one may be two centimeters which is not much whilst dealing with elements of 20 meter length or even longer and 15 tons weight or even more.
Assembly teams trained in erection of huge steel structures often command a good understanding of the assembly process and the prerequisite skills for the installation of precast concrete structures.
Half Ready Made Parts
It is not always commendable to provide fully concreted elements to the site. Half ready-made slabs often combined with beam-like extensions allow to save transportation costs and to activate continuity effects.
The precast slabs act as a lost formwork and can be combined with on-site concrete via rough surfaces and special shear reinforcement.
This technology is very common with residential, commercial and office buildings with multiple floors.
Field Factories
The production of precast elements in temporary on-site workshops helps in combining the advantages of precast technology whilst avoiding the expensive – sometimes even impossible – transport of huge elements. This strategy comes to mind whenever the amount of required elements allows for setting up shop with all the necessary tools like gantry cranes, mixing units and many more.
Field factories have been widely used in Central Europe after World War II, preceding the installation of full-fledged factories.
Planning and planning Tools
As there is almost no means to change the shape of precast concrete elements, but within very narrow limits only, precise and reliable planning gains crucial importance.This is good news in terms of quality assurance, where no detail should be left to chance anyhow. The laborious and time-consuming process pays back with a thorough control of production and assembly leading to smooth and swift erection and high satisfaction of the investors.
The design process can and might be supported by a range of specialized, often highly sophisticated software. As far as my personal experience goes there is currently nothing available which could replace human planning capacities in any way. The structural design demands a good understanding of the geometry interrelation with focus on stabilization and local stability.
The design of the workshop drawings is an arduous task requiring persistent focus and sound structural understanding. So far we have made great experiences with young Indian engineers which are able to tackle the task having gone through a thorough and detailed education.
Range and Limitations
Precast concrete elements can be employed most beneficially in the context of widespread buildings with a focus on industrial and commercial facilities.
Once the initial investment has been undertaken and a ready production unit has been set up – no small feat for sure – a wide variety of customers can be supplied. Where the market participants are not aware of the technology,education and even schooling needs to be provided. As the proper employment of precast concrete members has some impact on all stages of a project, from architecture and structural design through execution and maintenance.
Precast concrete technology is first choice where heavy loads, wide spans and attractive appearance are required. They can be designed in a way that ensures high fire resistance as well as explosion resistance.
Severe seismic impact remains a challenge for precast concrete members. The elements as such can effortlessly deal with dynamic loads – their joints not so well. One needs to resort to expert designs and some additional measures on site, which might result in in-situ welding or heavy-duty threaded connections.
The logistic task of producing concrete elements and members is quite challenging. One needs scaffolding, formwork, steel in various shapes and the ingredients of course, mainly sand, water, and cement– together with a reasonably educated labor force and the unavoidable planning.
Even though there is no feasible alternative to reinforced concrete at our disposal. Thus we would need to consider the optimization of the building process with concrete.
Execution On-site
The limitations of on-site execution are more than obvious: all necessary materials and labor need to be moved to the building site, all steps of execution are to be performed in place. There is only so much which can be done in one step of execution. That includes the setup of the formwork, the preparation and placement of reinforcement and built-in parts and the procurement and pouring of the concrete. All works and trades are done once and can be reused to a minor extent only.
Thus execution of on-site concrete parts tends to be slow and inefficient. The exposition to wind and weather often in perilous altitudes does not encourage for quality and quality control. The need of concreting upright members in-situ and the limitation of what can be mixed in place cause many casting segments thus leading to ugly seams and increase of the structural risks.
Factory Production
The production of concrete elements in factories provides an abundance of advantages which come with the setup of stationary processes: All tools and materials are easily available and can be maintained and provided in a continuous, well established process. Skilled workforce can settle down close to their daily working area. Working in shifts may contribute to a higher exploitation of the investments undertaken.
The conditioned environment allows for optimal procedures and continuous quality control including the requisite documentation of each and every production step. Higher concrete grades improve the structural rigidity and shorten the curing process.
All members can be done in horizontal formwork. Formwork – preferably in steel – which can be used many a times, even for years, providing a smooth and seamless surface and a precision which is simply not achievable on site.
Pre-stressed trusses can bridge over 30 meters and have become quite popular with the investors in logistic buildings where any columns are obstacles to the workflow only.
Transport and Assembly On-site
Concrete members tend to be heavy. The removal out of the formwork and the handling in the factory require powerful and reasonably fast moving cranes.
There is a limit to the maximum size and weight of parts which can be brought to site and assembled over there. It is advantageous on the other hand to reduce the number of elements thus saving assembly steps and joints and providing the desired column-free handling areas.
These dimensions depend on the available infrastructure and traffic regulations. Wall and slabs of up to 4 m height, lengths of 10 m and thicknesses up to 25 cm are common in Central Europe. Columns of a 20 m length and more come with their complete foundation in one piece. Considering the recent and remarkable improvement in India’s infrastructure comparable dimensions should be in range of feasibility.
The assembly requires precise survey and installation. The tolerances are less than one may be two centimeters which is not much whilst dealing with elements of 20 meter length or even longer and 15 tons weight or even more.
Assembly teams trained in erection of huge steel structures often command a good understanding of the assembly process and the prerequisite skills for the installation of precast concrete structures.
Half Ready Made Parts
It is not always commendable to provide fully concreted elements to the site. Half ready-made slabs often combined with beam-like extensions allow to save transportation costs and to activate continuity effects.
The precast slabs act as a lost formwork and can be combined with on-site concrete via rough surfaces and special shear reinforcement.
This technology is very common with residential, commercial and office buildings with multiple floors.
Field Factories
The production of precast elements in temporary on-site workshops helps in combining the advantages of precast technology whilst avoiding the expensive – sometimes even impossible – transport of huge elements. This strategy comes to mind whenever the amount of required elements allows for setting up shop with all the necessary tools like gantry cranes, mixing units and many more.
Field factories have been widely used in Central Europe after World War II, preceding the installation of full-fledged factories.
Planning and planning Tools
As there is almost no means to change the shape of precast concrete elements, but within very narrow limits only, precise and reliable planning gains crucial importance.This is good news in terms of quality assurance, where no detail should be left to chance anyhow. The laborious and time-consuming process pays back with a thorough control of production and assembly leading to smooth and swift erection and high satisfaction of the investors.
The design process can and might be supported by a range of specialized, often highly sophisticated software. As far as my personal experience goes there is currently nothing available which could replace human planning capacities in any way. The structural design demands a good understanding of the geometry interrelation with focus on stabilization and local stability.
The design of the workshop drawings is an arduous task requiring persistent focus and sound structural understanding. So far we have made great experiences with young Indian engineers which are able to tackle the task having gone through a thorough and detailed education.
Range and Limitations
Precast concrete elements can be employed most beneficially in the context of widespread buildings with a focus on industrial and commercial facilities.
Once the initial investment has been undertaken and a ready production unit has been set up – no small feat for sure – a wide variety of customers can be supplied. Where the market participants are not aware of the technology,education and even schooling needs to be provided. As the proper employment of precast concrete members has some impact on all stages of a project, from architecture and structural design through execution and maintenance.
Precast concrete technology is first choice where heavy loads, wide spans and attractive appearance are required. They can be designed in a way that ensures high fire resistance as well as explosion resistance.
Severe seismic impact remains a challenge for precast concrete members. The elements as such can effortlessly deal with dynamic loads – their joints not so well. One needs to resort to expert designs and some additional measures on site, which might result in in-situ welding or heavy-duty threaded connections.
