Introduction to building foundations: basic structures of doors, stairs, and roofs

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An introduction to building foundations: the basic structure of doors, stairs, and roofs. The structure of doors: Sliding wooden doors are the most commonly used type in current civil buildings; they consist of a door frame, door leaf, jambs, and hardware components. Common types of door leaves include the following: Panel-mounted door leaves: This is the most commonly used type of door leaf, suitable for both interior and exterior doors. It consists of a frame made up of a border and upper, middle, and lower protrusions; glass is inserted into this frame, and a door core panel is placed at the bottom, resulting in what is known as a glass panel door. The core board can be made from materials such as wood planks, plywood, and fiberboard. Maintain a 5mm gap between the door leaf and the floor. Plywood door leaf: It is constructed with a frame made of smaller square timbers, plywood attached to both sides, and edged with small wooden strips around the perimeter. Plywood doors have a simple construction, a smooth surface, and are easy to open and close. They allow for the use of small and short pieces of wood, thus conserving timber; however, they are not resistant to moisture and sunlight. Therefore, rooms such as bathrooms, toilets, and kitchens are not suitable for use, and they are mostly used for interior doors. Panelled door leaves: The construction is similar to that of panelled doors; a wooden frame is first made, and the door core panel is composed of multiple wooden strips glued together. The narrow boards are grooved so that each board can expand and contract freely to adapt to changes in outdoor climate. Panelled door leaves are commonly used for the doors of industrial buildings. Stairs (1) Types of stairs: Stairs are facilities that provide access between different floors of a building, and they are usually located near the entrance and exit of the building. There are also some stairs located outdoors. The advantage of outdoor stairs is that they don’t take up any indoor space; however, in cold regions where snow and ice tend to accumulate, they are not suitable for use. Stairs can be classified into indoor stairs and outdoor stairs based on their location. Based on their usage, they are classified as follows: interior stairs include main stairs and auxiliary stairs, while exterior stairs include safety stairs and fire-resistant stairs. Classified by materials used: wooden stairs, reinforced concrete stairs, and steel stairs. Based on their layout, stairs can be classified into single-flight stairs, double-flight stairs, triple-flight stairs, as well as split and combined double-flight stairs. Single-flight stairs: When the floor height is low, single-flight stairs are often used, starting from the bottom floor and leading directly to the upper floor in one direction. It has only one flight of stairs with no landing in the middle; therefore, the number of steps should not be too large, and it is not suitable for houses with high ceilings. Double-flight stairs: This is the most widely used type. Between the two floor levels, there are two parallel stairways moving in opposite directions and an intermediate landing. Often, two flight of stairs are made equal in length to save space. Three-flight staircase: Located between two floor levels, it consists of three flight of stairs and two landing platforms; it is commonly used in buildings with large floor heights, and an elevator shaft can be installed in its center. Split and combined staircases: In a split staircase, there is one wider flight of stairs that leads to a landing, from which two narrower flights of stairs continue upward to the floors. Unlike the double combination type, it first involves ascending two narrower flight of stairs to a landing, before combining into one wider flight of stairs to reach the floor. (2) Composition of stairs: A stair consists of flight steps, landings, railings, and handrails. Stair flight: It is an inclined element that connects two platforms at different elevations, consisting of a continuous series of steps. Its width should be determined based on the volume of foot traffic, the movement of furniture and equipment, and the principles of safe evacuation. Its maximum slope should not exceed 38 degrees; a range of 26–33 degrees is more appropriate. Rest platform: Also known as an intermediate platform, it is a platform located between two floors. When there are more than 18 stair steps, a landing should be installed in the middle to serve as a place for rest and relief. The rest platform consists of a girder and a deck. The depth of the platform should ensure that the net width after installing the radiators is not less than the width of the stair section, to facilitate passage and the movement of furniture. Railings, balustrades, and handrails: Railings and balustrades are protective structures installed at the edges of stairways and platforms to provide stability and safety. Typically, one side of a staircase section is against the wall while the other side faces open space. Handrails should be installed on the balustrades; their height should be approximately 900 mm above the steps. (3) Structure of stairs: Reinforced concrete stairs are the most widely used type of stairs today, offering high strength, durability, and fire resistance. Based on the construction method, it can be divided into cast-in-place and prefabricated types. Cast-in-place reinforced concrete stairs involve pouring the stair flights, landings, and landing beams on-site to form a single unit; they exhibit good integrity and strong seismic resistance. Depending on their structure, they are further divided into slab stairs and beam stairs. Slab staircase: It is a sloped slab, with its ends supported by platform beams, which in turn are supported by brick walls. Beam staircase: refers to a staircase type in which diagonal beams are installed on both sides of the stair treads, with these diagonal beams resting on the platform beams. The load is transmitted from the tread plates to the diagonal beams, and then from those beams to the platform beams. The use of precast reinforced concrete stairs helps to increase the degree of industrialization in construction, improve working conditions, and speed up the construction process. Based on the form of prefabricated components, they can be divided into two types: small-component assembly type and large-component assembly type. Modular staircase with small components: This type of staircase involves prefabricating the steps, diagonal beams, platform beams, and platform slabs separately, before assembling them together. This type of step is supported by brick walls rather than diagonal beams; it can be installed as the bricks are laid, without the need for lifting equipment. Prefabricated stairs with large components: These stairs are composed of prefabricated stair treads, landing beams, and landing slabs. The inclined beams and tread plates can be combined into one unit, and the platform boards and platform beams can also be formed into a single slab, which are then lifted onto site using lifting equipment. Roof (1) Functions and requirements of the roof: The roof is the uppermost covering of a building, consisting of the roofing surface and the supporting structure. The protective function of the roof is to prevent the intrusion of rain, snow, wind and sand from nature, as well as the effects of solar radiation. On the other hand, it must also bear the loads on the upper part of the roof, including wind and snow loads, the weight of the roof itself, as well as the weight of any components or people present, and transfer these loads to the walls. Therefore, the roof is required to be strong and durable, have a low weight, and possess properties such as water resistance, fire resistance, heat retention, and insulation. At the same time, it is required that the components be simple, easy to construct, and able to integrate with the overall building, while also having a good appearance. (2) Types of roofs: Based on their shape, roofs can be broadly divided into four categories: flat roofs, pitched roofs, curved roofs, and multi-pleated roof panels. Flat roof: The maximum slope of the roof surface is no more than 10%; the slope commonly used in residential buildings is 1%–3%. Generally, cast-in-place and precast reinforced concrete beams and slabs are used as the load-bearing structure, while the roof is treated for waterproofing and insulation. Pitched roof: The roof has a relatively steep slope, exceeding 10%. There are various forms such as single-slope, double-slope, four-slope, and hip-and-gable styles. A single slope is used for buildings with short spans, while double and four slopes are used for buildings with longer spans. Trusses are commonly used as load-bearing structures, while tiles are used for roofing. Curved roofs: The roof surface takes on various curved shapes, such as spherical or hyperbolic paraboloid shapes. Load-bearing structures include grid structures, reinforced concrete monolithic thin shells, suspension structures, etc. Multi-wave folded plate roof: It is a type of multi-wave roof made from thin reinforced concrete slabs. The thickness of the folded plate is approximately 60 mm. The wavelength of the folded plate is 2–3 meters, and its span ranges from 9 to 15 meters. The inclination angle of the folded plate is between 30 and 38 degrees. Based on the cross-sectional shape of each wave, there are two types: triangular and trapezoidal.