Chapter 19 Floors

Objectives After reading the chapter and reviewing the materials presented the students will be able to: Distinguish between the types of frame superstructures. Describe the process of installing beams, girders, and posts. Identify the framing members of a floor frame. List the steps for installing subflooring.

Types of Superstructures The superstructure is the part of the building that is above the foundation. Mass superstructures: are solid with little or no open space inside them. Hydroelectric dams are an example of a steel reinforced mass superstructure. Bearing Wall Superstructures: are buildings that have thick walls made stone or brick held together with mortar. Today, bearing walls are seldom used in buildings with more than two stories. Frame Superstructures: have a skeleton made of wood, reinforced concrete, or steel. Most modern buildings have frame superstructures. The basic components of a frame superstructure are the floors, columns, and ceiling or roof. Wood frames are used in one to four storey buildings. Reinforced concrete frames are used in multi storey buildings. The tallest buildings use steel frames.

Types of Superstructures Steel Reinforced Concrete Frame Superstructures: are either cast in place on the site or precast at a manufacturing plant and then transported to the site. At the site precast sections are put in place using a crane (fig 19-7, page 326). Structural Steel Frame Superstructures: make it possible to build skyscrapers and large bridges. The steel frame provides a high strength to weight ratio and provides more fire resistance than a wood frame. Structural steel is joined by using welding and bolting.

Fabric Superstructures Fabric is now used for sports arenas, music venues, and art centers. Air supported structures are supported by air pressure (fig 19-8, page 326). Tensile structures use fabric over a frame composed of strong poles and heavy cable.

Platform Floor Frames Platform framing is a framing system in which the first floor is built on top of the foundation wall as a platform. Installing Beams, Girders, and Posts: Buildings wider than 25 feet must have a steel I beam, wood girder, or bearing wall approximately one half distance between the outside walls. Jack Posts: are adjustable supports for I beams or wood girders. Either wood or steel posts are used to support girders. Installing Sills: The sill is the lowest portion of the frame of a structure (fig 19-14, page 329). It is attached to the foundation wall by anchor bolts and supports the frame of the building. Sill sealer: is a barrier installed between the top of the foundation wall and the sill to fill any gaps that might allow heat transfer into or out of the building.

Spacing & Span of Joists Determines Size Span is the distance between vertical supports. Dead Load is the weight of the structure including all fixed components of the structure. Live Load is the weight of any movable objects within a structure. Extensive testing has been done to determine the maximum allowable span for various species, grades, and sizes of joists (fig 19-15, page 330). They must be used to determine joist sizes.

Installing Stringers, Joist Headers, and Joists Stringers and joist headers sit on top of the sill and extend all the way around the sill (fig 19-16, page 331). Once the stringer and joist header are installed, the floor joists can be laid out (fig 19-17, page 331). Local building codes dictate floor joist spacing. Openings may be needed in the floor frame for stairs, chimneys, fire-places, and other components. Trimmers are full length floor joists that reinforce rough openings in the floor frame. Bridging is a support system that holds the floor joists in a vertical position and distributes live loads to three or more floor joists (fig 19-21, page 334).

Installing Subflooring The final step in building the floor frame is to install the subfloor (fig 19-22, page 336). The purpose of the subfloor is to make the floor frame rigid; provide a base for finish materials such as carpet or hardwood flooring; and provide a platform for building walls or a roof. Building codes typically require nails to be driven every 6” to 8” along each joist.

Summary The superstructure is the part of the building that is above the foundation. Mass superstructures are solid with little or no open space inside them. Bearing Wall Superstructures: are buildings that have thick walls made stone or brick held together with mortar. Frame Superstructures: have a skeleton made of wood, reinforced concrete, or steel. Most modern buildings have frame superstructures. Steel Reinforced Concrete Frame Superstructures: are either cast in place on the site or precast at a manufacturing plant and then transported to the site. Structural Steel Frame Superstructures: make it possible to build skyscrapers and large bridges. The steel frame provides a high strength to weight ratio and provides more fire resistance than a wood frame. Platform framing is a framing system in which the first floor is built on top of the foundation wall as a platform. Installing Beams, Girders, and Posts: Buildings wider than 25 feet must have a steel I beam, wood girder, or bearing wall approximately one half distance between the outside walls. Jack Posts: are adjustable supports for I beams or wood girders. Installing Sills: The sill is the lowest portion of the frame of a structure. It is attached to the foundation wall by anchor bolts and supports the frame of the building. Dead Load is the weight of the structure including all fixed components of the structure. Live Load is the weight of any movable objects within a structure. The final step in building the floor frame is to install the subfloor.

Home Work 1. Why is structural steel frame used for skyscrapers? 2. What is dead load?