OBJ 3.2B Structural Choices

Question 1

Choose systems with simple floor and roof framing that are fabricated mostly on-site

Which structural system do you choose if you have a highly irregular form? (4)

Answer 1

1. Sitecast concrete using any slab system without beams or ribs, 2. Light Gauge Steel Framing 3. Platform frame 4. Masonry construction with either concrete slab or wood light floor framing

Question 2

Expose the structure while retaining a high fire resistance rating (3)

Answer 2

1. All concrete systems (although ribbed systems may require added thickness in the ribs or slab, or applied fireproofing) 2. Heavy timber frame 3. Mill construction

Question 3

Use systems that do not include beams or joists in the floor and roof structure

Allow column placements that deviate from a regular grid (2)

Answer 3

1. Sitecast concrete two-way flat plate or flat slab, 2. Metal Space frame

Question 4

Thinnest floor systems are concrete slabs without ribs, preferably prestressed

Minimize floor thickness (3)

Answer 4

1. Sitecast concrete two-way flat plate or flat slab, especially when post tensioned 2. Precast prestressed hollow core or solid slab 3 Post tensioned one-way solid slab

Question 5

Long span structural systems:

Minimize the area occupied by columns or bearing walls (9)

Answer 5

1. Heavy wood trusses 2. Glue-laminated wood beams 3. Glue-laminated wood arches 4. Steel frame 5. Open-web steel joists 6. Single-story rigid steel frame 7. Steel trusses 8. Sitecast concrete one-way joist or waffle slab, particularly when post-tensioned 9. Precast concrete single or double tees Specialty type: Specially fabricated steel beams, suspended systems, arches, vaults, and shells

Question 6

Consider short-span one-way systems that permit easy structural modification

Allow for changes in the building over time

Answer 6

1. Light gauge or conventional steel frame 2. Any wood system 3. Sitecast concrete one-way solid slab or one-way joist construction, excluding posttensioned 4. Precast concrete solid or hollow core slabs

Question 7

System that doesn’t depend on on-site processes and that can be erected quickly

Permit construction under adverse weather conditions

Answer 7

1. Any steel system 2. Any wood system 3. Precast concrete systems, particularly those that minimize the use of sitecast concrete toppings and grouting

Question 8

Choose column and beam systems supported on point footings, thereby minimizing excavation/Choose systems that rely on a high degree of off-site prefabrication to minimize construction activities on site

Minimize site disturbance

Answer 8

: 1. Heavy timber 2. Steel frame Choose longspan systems that minimize bearing elements, such as: 3. heavy wood trusses 4. glue-laminated wood beams 5. glue-laminated wood arches 6. open-web steel joists 7. steel trusses Choose systems that rely on a high degree of off-site prefabrication to minimize construction activities on site, such as: 8. single-story rigid frames 9. Any precast concrete system

Question 9

Consider systems in which the building is constructed on-site from easily formed, relatively unprocessed materials

Minimize off-site fabrication time

Answer 9

1. Any sitecast concrete system 2. Light gauge steel framing 3. Platform frame 4. Any masonry system

Question 10

Consider systems using highly preprocessed, prefabricated, or modular components

Minimize on-site erection time

Answer 10

1. Single-story rigid steel frame 2. Steel frame, particularly with hinge connections 3. Any precast concrete system 4. Heavy timber frame

Question 11

Consider systems that are lightweight and easy to form, or prefabricated and easy to assemble, such as:

Minimize construction time for a one- or two-story building

Answer 11

1. any steel system 2. Heavy timber frame 3. Platform frame

Question 12

The absence of lead time for the prefab of components in sitecast concrete systems allows construction of the building to begin on-site at the earliest time

Minimize construction time for a 4- to 20-story building

Answer 12

1. Precast concrete 2. Steel frame Once those above systems are prefabricated, on-site erection proceeds quickly. 3. Any sitecast concrete system The absence of lead time for the prefab of components in sitecast concrete systems allows construction of the building to begin on-site at the earliest time

Question 13

System that is strong, lightweight, prefab, and easy to assemble:

Minimize construction time for a building 30 stories or more in height

Answer 13

1. Steel frame 2. Precast and sitecast are economical alternatives to steel frame construction

Question 14

capability of economically forming rigid joints

Avoid the need for diagonal bracing or shear walls

Answer 14

1. Any sitecast concrete system, particularly those with beams, or deepened slabs around the columns 2. Steel frame with welded rigid connections 3. Single-story rigid steel frame When depending on a rigid frame for lateral stiffness, the sizes of the frame members often must be increased to resist the added bending stresses produced in such systems

Question 15

Consider lightweight or short-span systems:

Minimize the dead load on a foundation

Answer 15

1. Any steel system 2. Any wood system

Question 16

Frame systems without rigid joints:

Minimize structural distress due to unstable foundation conditions

Answer 16

1. Steel frame, with bolted connections 2. Heavy timber frame 3. Precast concrete system 4. Platform framing Welded steel frames, masonry bearing walls, and sitecast concrete frames are particularly to be avoided

Question 17

Consider systems that incorporate many of the functions of a complete wall system in one operation, such as:

Minimize the number of separate trades needed to complete a building

Answer 17

1. masonry construction, including mill or ordinary construction 2. precast concrete loadbearing wall panel systems

Question 18

Systems that naturally provide convenient hollow spaces

Provide concealed spaces for ducts, pipes, etc.

Answer 18

1. Light truss and open-web joist systems 2. Light gauge steel framing 3. Platform frame Light gauge steel framing and platform frame construction are often applied as finish or infill systems in combination with other types of building structures to provide such spaces.