Timber and Masonry
One of the concerns of professionals in the structural engineering community is the limited exposure to timber and masonry design for graduating civil/structural engineering majors. A majority of smaller scale structures are constructed using timber/masonry separately or a combination of these materials; yet most civil/structural engineering curriculums emphasize steel and concrete as building materials and provide less of a focus on timber and masonry design. Additionally, the timber industry has evolved beyond the typical traditional stick-framed construction to a more advanced and innovative building material, and many students will be unprepared to design buildings without this as part of their curriculum. As noted in prior STRUCTURE® articles, the National Council of Structural Engineers Associations (NCSEA) promotes a varied curriculum that includes a balance of analysis, design, and other technical skills. Timber and masonry design are an integral part of the recommended curriculum. And although NCSEA believes timber and masonry should each be provided as its own course, a timber/masonry material design curriculum can be organized into two modules: element design and building systems design. In the first module, the basics are introduced, such as: the properties of a given material, advantages and limitations of a given building material, design of beams (flexural), columns (axial and combined axial and bending), shear walls or structural panels, and diaphragms (where applicable). The second module links the use of building codes and standards, such as the International Building Code, American Concrete Institute’s Building Code Requirements for Structural Concrete, American Institute of Steel Construction’s Specification for Structural Steel Buildings, American Wood Council’s National Design Specification for Wood Construction, and Masonry Standards Joint Committee’s Building Code Requirements for Masonry Structures, with structural analysis to design small scale (and regular) buildings. The curriculum includes developing a framing system for both lateral and vertical loading to emphasize the concept of load path and to gain exposure to building irregularities in structural systems. Then there is determining the gravity and lateral loads to establish loading and design criteria, followed with designing beams, columns, structural panels, diaphragms, collectors, and connectors to resist gravity and lateral load requirements. Finally, there is the development of structural drawings (plans and connection details) to connect analytical work to the communication tool used for construction. The last step exposes students to a critical part of design, but also to constructability and building sequencing. Together, Module One and Module Two encompass the NCSEA Core Curriculum suggestions for Timber and Masonry. It’s envisioned that the first module is either a combined timber/masonry course, as currently offered at some institutions, or as two separate timber and masonry courses. Schools limited by a variety of constraints can implement Module One to expose students to both materials. Module One is sufficiently intense to provide a student with a basic understanding of both materials so that self-teaching can raise the student to a higher level of understanding. In either scenario, 60 (semester) lecture hours are proposed to introduce the basics of material design for wood and masonry. The second module would include the design of a regular building with the two materials, and a comparative study of using either masonry or wood as the lateral load resisting elements, such as shear walls. Although this module may be more demanding, 60 lecture or contact hours are foreseen as a minimum to cover the recommended material.▪
Suggested Timber/Masonry Module Two
1) Building configuration
2) IBC load requirements (gravity and lateral)
3) Selection of roof and floor systems
4) Preliminary design process
5) Structural design computations using allowable stress design (ASD) for timber and LRFD for masonry, then develop working drawings (notes, plans, elevations, details) for structural systems including:
a. floor framing – sawn lumber, I joists, manufactured lumber, glulams, etc.
b. roof framing – sheathing, stick framing, prefab trusses, tiebacks/anchorage etc.
c. wall framing – sheathing, studs, posts, headers, masonry, trim requirements at openings etc.
d. shear walls – sheathing/block selection, chords, connections, segmented, perforated (optional) for plywood and masonry, etc.
e. diaphragms – sheathing, chords, collectors, sub-diaphragms, cross-ties, flexible vs. rigid, cantilever, etc.
6) Configuration & design of connections
Suggested Timber/Masonry Module One
1) Wood Buildings and Design Criteria using allowable stress design (ASD)
2) Properties of Wood & Lumber Grades
3) Beam & Joist Design – Sawn Lumber, Glued Laminated Timber, Manufactured Lumber
4) Stud & Column Design – Axial members (buckling versus crushing) and combined axial and bending
5) Shear Wall Design – Segmented and perforated wall concepts. Calculations for segmented wall method only
6) Diaphragm Design – Sheathing, chords and collectors for flexible diaphragms
7) Connector capacity – Behavior and capacity of nails and bolts
8) Masonry Buildings and the history of masonry as a building material, ASD versus LRFD
9) Construct-ability, sequencing, and terminology for masonry construction, material strengths and lab testing
10) Beam Design (LRFD) – flexural model, failure modes, shear requirements, deflections using cracked section properties
11) Column/Pilaster Design – role of longitudinal and transverse, pure axial and combined axial and bending
12) Shear Wall design – in-plane design for shear, flexure, and introduction of the axial-moment relationship
13) Wall Design – out of plane design, including second order effects
