Box Beams ARCH 544 Wood Structures Trevor Chou Ryan Lawson - PowerPoint PPT Presentation

Box Beams ARCH 544 – Wood Structures Trevor Chou Ryan Lawson

Background

Box Beam Structure • Dimension Lumber for top & bottom flanges & stiffeners • Structural panels for webs • Panel joints offset for optimal continuity of beam webs • Stiffeners act as shear splices for panel joints & resist web buckling • Should be spaced no more than 4 ft apart Source: “Data File: Nailed Structural-Use Panel and Lumber Beams Z416.” APA Wood , APA - The Engineered Wood Association, Feb. 2009, www.apawood.org/publication- search?q=Z416&tid=1.

Advantages of Box Beams • Longer spans than dimension lumber • High strength and stiffness • No shrinkage, warping, or twisting • Light weight • Easy to fabricate • Constructed of readily available materials • Open interior allows for insulation Source: “Data File: Nailed Structural-Use Panel and Lumber Beams Z416.” APA Wood , APA - The Engineered Wood Association, Feb. 2009, www.apawood.org/publication- search?q=Z416&tid=1.

Standard Box Beams • Tables available for sizing beams • Give allowable loads in lbs/ft • Multiple lumber sections can be used for flanges to increase flexural capacity • Thicker panel sizes provide higher shear capacities Source: “Data File: Nailed Structural-Use Panel and Lumber Beams Z416.” APA Wood , APA - The Engineered Wood Association, Feb. 2009, www.apawood.org/publication- search?q=Z416&tid=1.

Box Beam Design

Design Specifications • NDS for Wood Construction • Panel Design Specification (D510)

Connection Design • NDS Section 12 – Dowel Type Fasteners • Withdrawal Design • Lateral Design • Critical for Box Beam Design • Capacity taken as lowest value of all possible yield modes from Table 12.3.1A

Connection Design: Lateral Design Values Source: NDS: National Design Specification for Wood Construction . American Wood Council, 2018.

Connection Design: Yield Modes Single Shear Connections Double Shear Connections Source: Koch, Lori, and Adam Robertson. “Connection Design Examples Using the 2015 NDS (DES345).” American Wood Council , American Wood Council, www.awc.org/education/main/lists/des-design-considerations/des345-2015-nds-connection-primer.

Connection Design: Lateral Design Terms Source: NDS: National Design Specification for Wood Construction . American Wood Council, 2018.

Connection Design: Nail Dimensions Source: NDS: National Design Specification for Wood Construction . American Wood Council, 2018.

Connection Design: R d Source: NDS: National Design Specification for Wood Construction . American Wood Council, 2018.

Connection Design: F em Source: NDS: National Design Specification for Wood Construction . American Wood Council, 2018.

Connection Design: F es Source: NDS: National Design Specification for Wood Construction . American Wood Council, 2018.

Connection Design: F yb • Dowel Bending Yield Strength • Determined per Section 12.3.6 • Taken as 100,000 psi Source: NDS: National Design Specification for Wood Construction . American Wood Council, 2018.

Connection Design: Lateral Design Value Tables Source: NDS: National Design Specification for Wood Construction . American Wood Council, 2018.

Connection Design Calcs : (Single Shear) �� • Mode I M = 299 lbs � � • Mode I S = 50 lbs Controls � • Mode II = 102 lbs � � � • Mode III M = 111 lbs �� �� • Mode III S = 58 lbs � �� �� • Mode IV M = 82 lbs � � � Sources: • Koch, Lori, and Adam Robertson. “Connection Design Examples Using the 2015 NDS (DES345).” American Wood Council , American Wood Council, www.awc.org/education/main/lists/des-design-considerations/des345-2015-nds-connection-primer. • NDS: National Design Specification for Wood Construction . American Wood Council, 2018. • “Panel Design Specification D510.” APA Wood , APA - The Engineered Wood Association, May 2012, www.apawood.org/publication-search?q=D510&tid=1.

Mechanics of Materials: Nails • Allowable Load for Nail Shear: ��� ������� � ���� � ���� ����� ��� ����� ������� ��� � ��� ��� � ��� � � ���� ����� ��� ������� Sources: • NDS: National Design Specification for Wood Construction . American Wood Council, 2018. • “Technical Topics: Nailed Box Beam Design Example TT-116.” APA Wood , APA - The Engineered Wood Association, 20 Nov. 2014, www.apawood.org/publication-search?q=tt116.

Mechanics of Materials: Bending • Moment of Inertia: � � � � � • ������� �� � � � � • ���� �� • ����� ������� ���� • Allowable Load for Bending: ��� � ������� ��� � ��� � � ������� ������� ��� ��� � ��� � ��� ��� Sources: • NDS: National Design Specification for Wood Construction . American Wood Council, 2018. • “Technical Topics: Nailed Box Beam Design Example TT-116.” APA Wood , APA - The Engineered Wood Association, 20 Nov. 2014, www.apawood.org/publication-search?q=tt116.

Mechanics of Materials: Bending • Allowable tension stress, f t , should be used in bending equation: • Bottom chord is in pure tension, and allowable tension stresses control over allowable compression stresses. � � ������� ��� Sources: • NDS: National Design Specification for Wood Construction . American Wood Council, 2018. • “Technical Topics: Nailed Box Beam Design Example TT-116.” APA Wood , APA - The Engineered Wood Association, 20 Nov. 2014, www.apawood.org/publication-search?q=tt116.

Mechanics of Materials: Web Shear • First Moment of Area: � � � • 𝑅 ������� = 𝑐 � 𝑢 � � − � � � � � � � • 𝑅 ��� = 𝑢 � � = � � • 𝑅 ����� = 𝑅 ������� + 𝑅 ���� • Allowable Load for Web Shear: ��� ����� � � ����� � ��� � � � ����� ����� � ����� ��� ��� ����� � ��� ��� � ��� Sources: • NDS: National Design Specification for Wood Construction . American Wood Council, 2018. • “Panel Design Specification D510.” APA Wood , APA - The Engineered Wood Association, May 2012, www.apawood.org/publication-search?q=D510&tid=1. • “Technical Topics: Nailed Box Beam Design Example TT-116.” APA Wood , APA - The Engineered Wood Association, 20 Nov. 2014, www.apawood.org/publication-search?q=tt116.

Box Beam Allowable Load: • Bending: P max = 2185 lbs Bending Controls • Web Shear: P max = 2305 lbs • Nail Shear: P max = 2383 lbs

Testing

Box Beam Construction Sources: “Data File: Nailed Structural-Use Panel and Lumber Beams Z416.” APA Wood , APA - The Engineered Wood Association, Feb. 2009, www.apawood.org/publication- search?q=Z416&tid=1.

Test Set Up

Test Set Up

Testing

Results

Results Deflection (in) Load (lbs) Load vs Deflection of Box Beam Load Test 0 0 7000 1/16 750 6000 3/16 1000 4/16 2000 5000 6/16 2750 Load, P (lbs) 4000 8/16 3000 9/16 3750 3000 10/16 4000 2000 12/16 4250 13/16 4750 1000 14/16 5000 0 15/16 5225 0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 Midspan Deflection, Δ (in) 24/16 5500

Results • Failed due to Shear Buckling in the Webs followed by crushing of the structural panel at nail connections and disconnect of the structural panel from the nails • Allowable design calculations showed bending to control • Discrepancies likely lie in the inherent uncertainty in material properties • Failure occurred at 4000 lbs (point at which popping first occurred) • Test continued to 5500 lbs to visually see failure mode • Safety Factor:

Thank You!

Sources • “Data File: Nailed Structural-Use Panel and Lumber Beams Z416.” APA Wood , APA - The Engineered Wood Association, Feb. 2009, www.apawood.org/publication- search?q=Z416&tid=1. • Koch, Lori, and Adam Robertson. “Connection Design Examples Using the 2015 NDS (DES345).” American Wood Council , American Wood Council, www.awc.org/education/main/lists/des-design-considerations/des345-2015-nds- connection-primer. • NDS: National Design Specification for Wood Construction . American Wood Council, 2018. • “Panel Design Specification D510.” APA Wood , APA - The Engineered Wood Association, May 2012, www.apawood.org/publication-search?q=D510&tid=1. • “Technical Topics: Nailed Box Beam Design Example TT-116.” APA Wood , APA - The Engineered Wood Association, 20 Nov. 2014, www.apawood.org/publication- search?q=tt116.