In this blog post, we will examine how modern architecture has evolved in terms of scale and complexity, and briefly explain the principles and construction process of the mega truss structure and the lift-up-sliding method applied to Seoul National University’s “Kwanjeong Library.”
Reasons for Increased Scale and Structural Changes in Modern Architecture
Modern buildings are becoming increasingly larger and taller. The desire for larger and taller structures is filling the sky with buildings, and the competition to build high-rises has continued since it began in the United States in the late 19th century. The term “skyscraper” was used to describe these structures, and more recently, the term “mega-structure” has also emerged. You can also find massive buildings recently constructed on the Seoul National University campus; a prime example is the “Gwanjeong Library.”
First, let’s revisit the traditional concept that existed before high-rise buildings became widespread. When we imagine a building, we typically picture a rectangular prism with six sides; this is called a wall-bearing structure. In a wall-bearing structure, vertical members (walls) and horizontal members (ceilings and floors) support the load. Because construction is relatively quick and simple, this method is still used in many residential spaces, such as apartments. However, as buildings grow larger and taller, wall-bearing structures reach their limits. This is because as the load increases, the walls must become thicker to ensure stability, and as the walls get thicker, the interior floor area decreases and costs rise.
To solve this problem, the moment-resisting frame structure was introduced. Unlike the wall-based structure, which relies on planar members, the moment-resisting frame structure supports the building using linear members such as columns and beams. It’s easier to understand if you imagine a rectangular prism where the faces have disappeared and only the lines remain. When steel is used for these linear members, it becomes the steel-frame structure we are familiar with, enabling the construction of taller and more stable buildings. The steel-frame structure also offers the advantage of relatively easy construction and high interior design flexibility, as interior walls do not serve a structural purpose.
Steel is strong in resisting compression and tension but is weak against bending. Generally, since buildings rise vertically, considerations regarding bending are relatively low—except for special factors like wind loads or differential settlement—making steel suitable for use. However, when a building’s scale reaches the level of a megastructure, issues related to size, bending, and deflection in the horizontal direction become impossible to ignore. In such cases, the structure evolves into a truss structure to effectively control bending.
A truss structure consists of linear members connected in a triangular pattern, incorporating not only horizontal and vertical members but also diagonal members. This arrangement transfers moments caused by bending into axial forces (compression and tension), ensuring that the structure primarily承受s only axial forces without bending. As a result, the structure is resistant to deformation and maintains a stable form. Truss structures are commonly found in bridges and domes subjected to bending forces, and the ‘Kwanjeong Library’ on campus also utilizes a truss structure.
The Mega Truss and Lift-Up-Sliding Method of Seoul National University’s ‘Kwanjeong Library’
Looking at the structural diagram of Seoul National University’s ‘Kwanjeong Library,’ one can see that four rows of trusses (Mega Truss) are supported by five columns (Mega Column), creating a structure that appears to float in the air. During the design phase, the Kwanjeong Library was conceived as a structure partially superimposed atop the existing Central Library, leading to the adoption of this massive truss and column system. The challenge was how to hoist this heavy and massive structure onto the existing building.
In typical steel construction, a tower crane is used to lift steel members onto the columns and connect the joints. However, in the case of the Gwanjeong Library, the maximum span between trusses reached 112.5 meters, and it was impossible to erect a crane capable of supporting such a load, making construction using conventional methods difficult. Therefore, the Lift-Up-Sliding method was selected.
The lift-up-sliding method involves first erecting the steel columns, then assembling the mega-trusses on the ground and hoisting them into place atop the columns. To facilitate this, temporary structures supporting the lift-up and sliding processes were installed separately on-site, and these were dismantled after the installation of all four trusses was completed. This approach allowed the massive structure to be safely installed atop the existing building.
Many people may simply have the impression that the Kwanjeong Library is “really big.” However, if you stand in the lobby and look up, you will notice the massive diagonal columns extending from the fifth to the seventh floors. Through this truss structure—so naturally concealed that it goes unnoticed unless you look closely—we realize that architecture is not merely composed of walls and floors.
As the scale of buildings increased, new challenges arose, and various technologies and structural systems were developed to address them. Modern architecture can be described as the result of the fusion of science and art, and the competition among high-rise buildings has moved beyond a simple race for height to encompass considerations of efficiency, safety, and aesthetic elements. The “Kwanjeong Library” is a prime example born from this trend, serving as a landmark of Seoul National University that showcases architectural history, technology, and aesthetic value. We hope that many more people will visit this library in the future to gain knowledge and generate new ideas within its walls.
