As the world’s population continues to grow and building/engineering technology becomes even more advanced, skyscrapers are cropping up in Kenya and all over the world. These behemoth buildings are breaking height records and incorporating complex designs and engineering – the Nairobi Global Trade Center Tower (GTC Tower), for instance, is currently the tallest building in Kenya and incorporates the HOSPCA design concept. So, you may have pondered, at least occasionally, how such tall structures are constructed to withstand natural forces and events as well as their own weight. Here is everything you need to know.

Preliminary to designing and building any skyscraper, numerous different elements need to be taken into account by structural engineers and architects. One of them, which is crucial because it affects the building’s ability to withstand natural forces, is the tensile properties of the structural components. Tensile characteristics define how materials respond to tension (pulling forces acting longitudinally along a structural component such as a beam).
A structural load is a force, deformation, or acceleration applied to structural elements. A load causes stress, deformation, and displacement in a structure. Structural analysis, a discipline in engineering, analyzes the effects of loads on structures and structural elements. An excess load may cause structural failure, so this should be considered and controlled during the design of a structure. Different types of loads can cause stress, displacement, deformation on a structure; which results in structural problems and even structural failure. Determining the total load acting on a structure is very important and complex.
Tall structures, such as the GTC Tower, require the efficient transmission of different types of loads from the point or surface on which they are applied to the foundation and subsequently to the ground.

First, let’s classify The loads in buildings and structures then in detail explore the different load types.

  • vertical loads
  • horizontal loads
  • longitudinal loads.The vertical loads consist of:
  • Dead loads
  • Live loads
  • Impact LoadsThe Horizontal Loads Consist of:
  • Wind loads
  • Earth-quake/ seismic loadsThe longitudinal Loads consist of:
  • Tractive Forces
  • Braking forces
  • These are considered in special cases of design.

Briefly, lets expound on some the different types of loads.

  • Dead Loads
    A dead load is primarily brought on by the weight of various materials, permanent partition walls, fixed permanent equipment, and structural parts themselves, such as the weight of roofs, beams, walls, and columns.
  • Live Loads/Imposed Loads
    Live loads are moving or movable loads that are neither accelerating nor impacting. These loads, which include the weights of mobile partitions or furniture as well as human traffic, etc., are presumptively generated by the building’s planned usage or occupancy.
  • Wind Loads
    Wind load is largely a horizontal load principally brought on by air movement in relation to the earth. In structural design, wind load must be taken into account, especially if the building’s height is greater than twice the dimension parallel to the exposed wind surface.
  • Seismic Loads
    Seismic loads are primarily caused by earthquakes or aftershocks, which agitate the structure. In most cases, earthquakes or aftershocks cause vibrations that change in magnitude and impose a load that changes direction and position. This means that seismic loads are dynamic in nature.

As an integral landmark in Nairobi’s ever-changing skyline, the GTC Office Tower commands a presence made possible by the permanent structural components that now call the Westlands address home and the temporary structures, such as scaffolds, used in the building’s constructions and have since been dismantled.
The office tower ticks all the boxes of an engineering masterclass, infusing unique designs that have perhaps only been sparingly utilized so far in the country. For instance, the building incorporates transfer beams in various locations with spans of up to 38 meters horizontally. (To put this size into perspective, an Olympic-size swimming pool measures 50 meters in length and 25 meters in width.) These enormous beams in which various columns are anchored are subjected to massive vertical loads that are transferred onto them.

Office Tower Structure
With a total of 41 accessible floors, a floor dedicated to mechanical equipment, and a helipad on the 43rd floor, the lower levels of the office tower and the structural elements that prop them up are indeed subjected to substantial vertical loads. This vertical height, coupled with the enormous horizontal spans (the office tower has structural spans of 9 meters) and different support configurations on the superstructure (section of the building above the podium), meant that substantial vertical loads had to be transferred to the equally huge horizontal spans, which range from 9-38 meters.
Ordinarily, this would mean that deep beams and enormous columns would have to be used to resist the massive loads. But this would usurp space that would otherwise constitute usable floor area. Thus, engineers introduced structural I-beams to avoid using extremely deep beams and large columns. For the vertical loads, steel I-sections were put in place, which were later encased in reinforcement bars, with in-situ concrete forming the outer cladding in what created reinforced concrete columns. Thus, the office tower’s columns consist of reinforcement steel bars and a core made up of steel I-sections.
In addition, the office tower’s facades comprise significant quantities of structural steel. The 38-meter-long pedestrian bridges, the elevator core guide rails, the roof covering, and spiral staircases are some other examples of additional structures that utilize structural steel.

Self-Raising Scaffolding
The construction of the office tower at the pace with which the process was carried out would again not have been possible without the use of steel, especially in the scaffold, which was probably the first self-raising scaffolding used in the construction of an entire tower in Kenya. The scaffolding was a structural steel frame of I sections and rectangular hollow section (RHS) with a self-hoisting mechanism. The self-hoisting mechanism accelerated construction, resulting in a high concrete cycle of 10 days.
Advantages and Disadvantages of Structural Steel
Advantages of structural steel

  • Smaller column sizes increased usable space
  • There is less vertical transportation of mass compared to equivalent reinforced concrete.
  • There is less workmanship on site
  • Easier control of verticality
  • Offsite fabrication

    Challenges of using structural steel

  • The heavy sections were fabricated and shipped from overseas for quality control and Quality assurance, especially welding and anchorage to the concrete.
  • This required a long lead time on orders, shipping, and local delivery
  • Any prefabrication required sourcing technicians and technology from overseas
  • Installation of the elements required a specialized technician