Transportation Geography and Network Science/Physical structures

Introduction

A physical structure is something that has been made or built from parts, especially a large building. It has a certain spatial function which safely withstands all kinds of normal loads in a building. In civil engineering, a structure is a system of supporting elements (beam, column, etc.) that can carry loads.

Aim of Structure

There are 3 aims for a physical structure:

(i) To serve the requirements of space applications. A building structure is not only a necessary condition for human social life but also the artificial environment of social life.

(ii) To resist the effects of natural and manual loads. Buildings are subject to various loads and other effects imposed by nature and human beings. Supporting these loads and effects is the main goal of structures. In detail, the building structure is to ensure that the building is not damaged and does not collapse, keeping the building with sufficient stability and serviceability for a long time.

(iii) To fully develop the work of building materials. A building structure is based on building materials (concrete, cement, etc.). The structure is an organic combination of various building materials.

Critical Structural Elements

Horizontal structural element

Slab: Slabs are the flat-shaped components that directly bear the load on the building structure. Generally, they have larger plane sizes with small thicknesses. Slabs belong to bent components. The upper load is transferred to beam or wall through the slab. Roofs are a type of slab.

Beam: Beams are line-type components that bear perpendicular loads in the vertical direction. They are supporting components between slabs and columns. Beams also belong to the bent components, bearing the load from slabs and passing them to columns.

Vertical structural element

Column and wall: Both columns and walls are load-bearing components used to resist compression. Columns are line-type components that bear loads parallel to their vertical axis direction. Walls are the vertical-supporting components, which withstand loads parallel to the wall direction.

Footing: Footings are underground structural components, which transmit the load from upper structures, such as columns and walls, to the ground. Like the other vertical installation components, footings are also a type of compression-resistant component.

Proposes for Structure

Civil engineers design structures to satisfy the following three requirements:

(i) Stability. Stability means that the structure should be able to bear all kinds of effects that may occur in the normal design, construction and use processes. Through these effects (such as earthquakes), the structure can still maintain the necessary overall stability and safety without collapse.

(ii) Serviceability. Serviceability refers to the normal use of building structures, structural components should remain good working performance, which should not affect the use due to deformation, cracks or vibration and other phenomena.

(iii) Durability. Durability refers to the building structure under normal use and maintenance circumstances. Structural components should have sufficient durability and maintain the building's functions until the design life, without resulting in serious corrosion of materials, weathering, cracking (when components of the protective layer are too thin or too wide) and other phenomena. Durability depends on the environment in which the structure is structured and the design life.

Structure Network

There are two main types of network-shape structure: frame structure and truss structure.

Frame

In construction, a frame structure is a structure composed of many beams and columns to withstand the full load of the building. As the traditional brick-wall-supporting structure is not able to bear the load from multiple floors. Frame structures are often used in high buildings. Except for its own weight, walls in frame structure will not withstand any additional load. In order to reduce the load on the frame, the non-load-bearing walls are usually light-weight walls. Common materials to erect a frame are steel, concrete, timber, and aluminium.

The advantages of frame structure are flexible space separated, low self-weight, saving material and better seismic effect than brick structure. Differ from the traditional brick-wall-supporting structure, frame structure enable a large area to be supported by long span. It is also very flexible to separate the space. The only thing needs to do is to add a light-weight wall.

However, frame structures also have their disadvantages. With the increment of floors, the load capacity of columns and footings will become extremely large. In fact, the columns and footings have their ultimate load capacities, which indicates that the floors are not able to grow infinitely. Another aspect is that a frame structure has no effective horizontal resistance. That may cause large deformations when considering the heavy wind load. Generally, the ultimate height of the frame structure is about 40 metres. Therefore, the most important disadvantage is that it cannot be used to build super-high-rise buildings.

Truss

A truss is an assembly of beams or other elements that creates a rigid structure. In structural engineering, a truss is a structure that "consists of two-force members only, where the members are organized so that the assemblage as a whole behaves as a single object". A "two-force member" is a structural component where force is applied to only two points. The grid structure of a truss has nodes and links, which is same as the elements of a network. A truss is usually regarded as a whole structure to carry the upper loads. This usage of a truss is similar to that of a beam or a slab. In a typical context, external forces and reactions are a set of nodes. As a result, the internal forces in the members are either tension or compression.

A space frame truss is a three-dimensional framework of members pinned at their ends. Due to its spatial grid structure, it cannot be treated as a simple plate structure.

The advantages of a truss are low self-weight and material savings, compared to the concrete beam with the same loading capacity.