Rapid urbanization and space constraints are forcing planners and architects to build taller buildings using a combination of materials and methods of construction to strike a balance between performance, quality, speed and economy
MB Bureau Report
Traditionally “steel structures” and “concrete structures” have always been two different worlds in structural engineering. However, the construction community is gradually realizing that each of the two materials has advantages and disadvantages and that often an optimal solution is found by combining both materials. This may be a combination of steel and concrete in an element as is the case in “Composite steel-concrete construction” or the combined use of concrete elements and steel elements in “Hybrid or Mixed construction”.
Rapid urbanization and space constraints are forcing planners and architects to build taller buildings using a combination of materials and methods of construction to strike a balance bet-ween performance, quality, speed and economy.
As the costs of construction and ongoing maintenance continue to rise, architects, engineers and general contractors need to design and build structures that incorporate the best features of each construction method. New construction technologies are emerging together with new products, such as high performance concrete, tilt up concrete walls, prefabricated metal buildings leading to an overall improvement of productivity in construction.
Traditionally, it was either RCC structures or pure play structured engineering solutions. Hybrid construction is the use of a combination of advanced building systems to construct a better building. Every material has special properties. Specific combinations of individual materials make it possible to create particularly high performance structures. A hybrid building or structure uses different construction materials (steel-wood, steel-concrete, concrete-wood, etc.). In hybrid construction, different materials are skillfully combined to ideally take advantage of their respective properties. Materials and techniques used in hybrid construction are usually decided based on several factors including, cost, visual appeal, structural integrity, natural re-sources and production time.
Hybrid or mixed construction should not be confused with composite construction. Composite is defined as different materials acting homogenously. In hybrid construction, the materials may work together or independently but will always provide advantages over the use of a single material.
Inherent Advantages of Hybrid Metal Buildings with Concrete
Pre-engineered metal buildings are increasingly recognized as reliable, aesthetically pleasing, energy efficient and cost-effective buildings with optimum functionality. With buildings requiring longer spans and bays, a pre-engineered metal building is the right choice. The spanning capacity of a metal building is significantly more than that of a wood, concrete or even a conventionally framed structure. This results in much more flexibility concerning floor space. Additionally, customizable column locations and depths offer adaptability to most floor plans. On the other hand, the greater number of support columns needed in concrete construction limits the moving of walls and partitions thus reducing the amount of useable square footage. Overall, metal buildings give the end-user more flexibility and customization for their final design.
Hybrid metal buildings combine the efficiency of metal building systems with conventional construction to provide the ideal solution for large-scale, complex projects. Metal construction functions in hybrid form when combined in construction with brick, tilt up, concrete, glass, wood etc. Hybrid buildings take advantage of all the benefits of engineered steel buildings and add traditional construction elements like tilt-up walls or architectural elements made of light-gauge steel or wood. For instance, both concrete and steel are easy to use in buildings to provide structural strength and fire protection. Concrete floor/ceiling slabs, with their extremely great mass, ensure good acoustic insulation. However, one perceived drawback to long-span steel floors is their tendency to “bounce” or develop unwanted dynamic characteristics. Because concrete tilt-up has better damping, it doesn’t bounce as much. Builders can limit the “bounce” in steel floors by limiting deflection using beams with a higher moment of inertia (i.e. deeper length) that will limit deflection. Steel members require less complicated foundation systems. This gains importance when soil stability is poor.Often, depending on the design needs, buildings are built with both concrete and steel for the best possibilities. It is not uncommon for buildings to incorporate concrete tilt-up in their lower portion and steel in the upper.
Hybrid metal construction allows the designer to combine the best attributes of steel and other materials to improve performance, economics and occupant satisfaction in a way that might not be possible using only one of the materials and its associated construction techniques.
The general construction market should realize the advantages of integrating site building with pre-engineered steel, modular construction and prefabrication. Hybrid construction is cost effective because it maximizes the beneficial structural and architectural advantages in using components made of different materials.
In terms of speed of construction, it’s very economical. Various studies claim that hybrid construction can save at least 20% of construction time. Using precast concrete and structural steel as dominant material in hybrid construction, onsite operations are considerably reduced. Further the time needed for field erection can be reduced by as much as 35%.
The hybrid building program saves approximately 20% of time in building construction, which in turn reduces the construction cost significantly. By combining pre-engineered materials with steel, hybrid structures substantially reduce design, material weights, fabrication and shipping costs for the complete building structure. Because of the substantial amount precise manufacturing and pre-assembly prep work done during the design and manufacturing process, there are considerable savings in costs of direct labor, equipment and construction site overhead.
The hybrid usage coupled with large span floors eliminates the need for interior columns thus increasing the interior layout flexibility. Also, hybrid systems have a very effective design profile that allows them to meet any heavy loading requirements.
Pre-requisites for Success
One of the most important aspects for the success of projects that are developed based on hybrid construction is the planning and development of the project. The close cooperation and commitment of architects, engineers, suppliers, fabricators and erectors, sharing knowledge through a BIM (Building Information Model) system and working as a team is critical to the success of a hybrid project. The general contractor should also be well versed in the advantages and limitations of all methods of construction to help determine the best approach for the project.
Steel and concrete hybrid structures appeared in the United States and Japan in the early 1960s due to its potential cost effectiveness. In Japan, construction contractors substituted reinforced concrete beams by steel beams in conventional reinforced concrete retailing stores to make longer floor span. In the United States, contractors substituted steel columns by reinforced concrete columns in conventional steel structures to reduce the material cost. Those early emerging hybrid buildings were however mostly low-rise and located in low seismic regions since the seismic performance of such hybrid system is much more complicated than that of steel structure or reinforced concrete (RC) structure.
In Mainland China, considerable structures of super tall buildings are hybrid although the seismic performance of hybrid structure is lack of verification by real earthquakes. There have been many types of steel-concrete hybrid structures developed in the world. The seismic performance of steel-concrete hybrid structure has not been acknowledged as well as RC structures or steel structures. However, recent studies including both experimental and analytical results indicate that the overall seismic performance of the structure meet the requirements.
A steel concrete hybrid frame-tube super-tall building structure with new type of shear walls to be built in a district of seismic intensity 8 in China was studied for its structural complexity and irregularity. Both model test and numerical simulation were applied to obtain the detailed knowledge of seismic performance for this structure. First, a 1/30 scaled model structure was tested on the shaking table under different levels of earthquakes. The failure process and mechanism of the model structure are presented here. Nonlinear time-history analysis of the prototype structure was then conducted by using the software PERFORM-3D. The dynamic characteristics, inter-story drift ratios and energy dissipation conditions are introduced. On the basis of the comparison between the deformation demand and capacity of main structural components at individual performance level under different earthquake level, the seismic performance at the member level was also evaluated. Despite the structural complexity and code-exceeding height, both experimental and analytical results indicate that the overall seismic performance of the structure meet the requirements of the Chinese design code.
Hybrid construction is used frequently in Europe for new multi-storey buildings. This was earlier the domain of cast in place concrete and structural steelwork. Precast concrete is ideally suited to hybrid construction as it may be readily combined with other materials. Precast concrete also reduces on-site operations. The reasons are less wet concrete to place, fewer loose reinforcing bars to set and dewer structural components with their formwork. There is also less construction noise to disrupt local communities. All of these reasons also create a safer working environment.
Pre-Engineered Steel Buildings and structures company Kirby Building Solutions Limited believes that now that there is growing acceptance for pre-engineered metal buildings in the country, there is also a huge market for hybrid cement and steel-fabricated buildings and multi-storeyed structures in India. The company currently has two manufacturing facilities in India near Hyderabad and in Haridwar and is setting up plant another plant in Gujarat to meet the growing business need.
Adoption of a hybrid form of construction ensures that the most appropriate technology and the best ideas of the designer, constructor and concrete producer are incorporated into aesthetically pleasing structures. There sulting structures are fast to build, energy efficient, and capitalize on the considerable advantages inherent in the range of concrete and steel construction techniques employed.