CE Design of Timber Structures. Trial FINAL EXAMINATION

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1 Name: University of California, Berkeley Semester 00x Department of Civil EngeergFall Instructor: S. A. Mah CE 4 -- Design of Timber Structures Trial FINAL EXAMINATION This examation is open book and notes. Please show all calculations and dicate all relevant assumptions. Unless dicated otherwise, typical California coastal climatic conditions and standard mill practices may be assumed. When doubt regardg lumber gradg, use WWPA rules.. (5). (0) 3. (0) 4. (5) 5. (30) HAPPY HOLIDAYS Total: (00) Problem a. While spectg a construction site you notice that the carpenters are usg extremely short nails to attached the diaphragm to the framg. The contractor says not to worry because these are 0d nails common nails as specified on the drawgs. Sure enough, the box they come says that they are 0 d common nails. You make them stop and change the nails, because... b. You also note that the contractor is stallg tongue and groove floor panels at a location on the drawgs which calls for a blocked diaphragm. The contractor says not to worry sce the code allows for tongue and groove panels or clips as alternatives for blockg. You say you are not sure if this is the case this situation, because... c. What are the ma differences between terior and exterior plywood? d. Above what equilibrium moisture content is it necessary to reduce the allowable stresses for most species of glulam? EMC =

2 CE 4 - Fal Exam Name: e. You notice on spectg a buildg you designed several years ago that the nuts on the bolted connections are now loose (but not danger of fallg off). Your colleague asks if the bolts should be re-tightened. You say... f. Describe what is meant by a "rigid" diaphragm. Problem The spacg of joists on a floor (not roof) system is 4 ches on center. The design floor load is 75 psf (total DL + LL). The dead load is about 0 psf. The floor is to utilize APA Rated Sheathg that conforms to APA Heavy Duty Floor recommendations. Indicate the required plywood grade, span ratg (PII), thickness(es), edge support requirements, and panel orientations for the floor sheathg. Please specify the table Breyer that you use for your design. Problem 3 The bolted connection shown below uses two rows of 5/8-ch diameter bolts with eight fasteners each row on each side of the splice. The load applied is due to dead plus roof live load. The wood members are Douglas fir-larch (No. ) and the ma member is 4 by 0 ches (nomal) dimension, while the two side members are x0's. The wood is itially wet and seasons place to an EMC = %. a. What is the load capacity provided by the bolts? b. What would this load capacity be if two separate side plates were used on each side? c. What is the mimum length of the side members considerg spacg between bolts for you answer to parts a and b? The applied load may be tension or compression. d. What is the stress the wood ma member? Consider the load you computed part b. How does this value compare to the allowable stress the wood? 4x0 - x0 (one on each side)

3 CE 4 - Fal Exam Name: Problem 4 The base of a chord a shear wall used to resist earthquake forces is attached to the supportg foundation by a standard commercially available metal bracket as shown below. The load the bracket is applied to the member eccentically so that the chord experiences tension plus bendg. Check the adequacy of the chord (only) for the load shown. You need not check the bracket, anchor rod or the bolts! The lumber is Douglas Fir - Larch, No.. Consider only the gross section of the chord. 4x4 Chord T = 000# ch Problem 5 The roof diaphragm the sgle level commercial buildg shown plan view below is to be designed for lateral loads. Plywood shear walls are located on all four perimeter elevations of the buildg. The uniformly distributed lateral loads on the diaphragm due to wd and earthquake are tabulated below. You may ignore gravity load effects for this problem (roof live loads are nomal, i.e., 0 psf). Direction/ Wd Earthquake Load Longitudal 350 plf 660 plf Transverse 350 plf 360 plf a. Is the UBC span-to-width ratio satisfied? Show allowable ratio! UBC Ratio: Yes No b. For the upper left hand corner of the buildg dicate required plywood thickness and grade, nailg schedule and blockg, if any. Check both directions of loadg! Be sure to dicate what diaphragm case(s) you are considerg. Draw a sketch to show your design and the location of all typical nailg. 3

4 CE 4 - Fal Exam Name: c. Indicate where the diaphragm blockg may be deleted (consider both directions). Draw a simple sketch. d. Compute the maximum diaphragm chord forces and dicate a sketch where they occur (do not size the members). e. Determe the shear flow (plf) walls "A" and "B" due to loadg the transverse direction. f. Fd the maximum axial force the "collector" attached to wall "A" due to transverse loadg. Wall "A" is symmetrically positioned on the exterior elevation of the buildg. Orientation of plywood panels (but 8 ft direction runs NS). Orientation of x Joists at 6 " o.c. 0' Wall "A" Wall"B" 60' 0' Other possible topics clude: Nailg: defitions, adjustments, connection design/evaluation, spacg Boltg: Loadg perpendicular to gra, spacg, etc. Design problem, for example, fd the required size and spacg of floor joists to carry a specified load. Carry the design all the way through. Load resistg systems: cantilever beam systems, lateral load resistg systems, etc. Beams: Other topics not covered previously 4

5 Solution to Practice Fal CE 4, Fall 008 Solution to Problem Part (a) Contractor is usg shortened 0d nails commonly referred to as short or plywood nails, which come three lengths: -/8, ¼ & -3/8-ches. These nails are typically used for attachg the non-structural elements, such as non-structural plywood to serve as tile backg. Because of their shallower penetration, short nails are less likely to split framg members, but are more likely to withdraw. Thus, they may not be used as a substitution to 0d common nails. Part (b) Tongue-and Groove or panel clips constitute edge support and cannot be used stead of blockg when the floor plywood is used as a diaphragm (which is the case almost always). The exception is when the diaphragm is -/8 ch thick -4- plywood with stapled T&G. Part (c) Exterior panels have a fully waterproof bond and are suitable for applications subject to long-term exposure to the weather or to moisture. Exterior plywood is made with nothg but waterproof glue and should always be used for any exposed application. Interior plywood, made with highly resistant glues, can actually withstand quite a bit of moisture. There is terior plywood made with IMG (termediate glue), which is resistant to bacteria, mold, and moisture, but no terior plywood is made for use outdoors. Part (d) EMC = 6% Part (e) It should be re-tightened. Connections fastened with shear plates or split rgs may become loose after shrkage takes place and separate, thus reducg the bearg area of the wood and its ability to resist loads. Impact and extent of the shrkage on the bolted connections should be carefully evaluated and, if periodic tighteng is required - it should be specified on the drawgs!!! Part (f) Diaphragms are permitted to be idealized as rigid or semi-rigid where the computed maximum - plane deflection of the diaphragm under lateral load is less than two times the average story drift of adjog vertical elements. /6/008 Page of 7 Ver.

6 CE 4, Fall 008 Solution to Problem S j TL DL!" 4 Joist spacg!" 75psf Total floor load!" 0psf Dead load LL!" TL # DL " 65$ psf Live load NOTE : Heavy Duty ratg has been removed from the APA Tables 005. Instead, Structural Use ratg is selected. C D!".0 Load duration factor (terior floor loads are dead and live) L 360 live load deflection limit and L 40 total load deflection limit Required floor span is 4", so use 48/4 span ratg. From APA Load-Span Tables for Structural-Use panels, Table a: L 360 live load deflection limit 9psf % 65psf OK L 40 total load deflection limit 86psf % 75psf OK Bendg strength: C D $ 94psf " 94$ psf > 75psf OK Shear strength: C D $ 67psf " 67$ psf > 75psf OK From the ASD Manual: edge support is not required for up to 36 ch spans From the ASD Manual Table C9..3 select 3/3 thick structural panel. Use 3/3 thick Structural Use panel with 48/4 span ratg, strong axis bendg, no edge support and contuous over 3 spans. /6/008 Page of 7 Ver.

7 CE 4, Fall 008 Solution to Problem 3 Note that shrkage is not a problem this connection, sce side members are made out of same wood and will shrk approximately the same. Part (a) This is a double shear connection for the bolts. See Example 3.5 for applicable equations. Note the capacity is provided by ONLY ONE side of the connection - that is time 8 = 6 bolts. These 6 bolts will resist the tension double shear wood-to-wood connection. Followg adjustment factors apply for Z: 5 D!" 8 Diameter of bolt Z F yb!" 45000psi!" 760lb From Table F for both members parallel to load n!" 8 N!" 6 Number of bolts Ma member: Douglas Fir-Larch, No, 4x0: l m!" 3.5 t m!" 3.5 F em!" 5500psi d!" 9.5 Side members: Douglas Fir-Larch, No, x0: l s!".5 t s!".5 F es!" 5500psi d s!" 9.5 Adjustments factors are: C t!".0 C di!".0 C eg!".0 C tn!".0 C M!" 0.4 For itially wet, then seasoned place C!".0 For base spacg requirements s!" 4D ".5$ Spacg between bolts a row γ!" 70000$ & ' ( D ) *+.5 lb $ " $ lb E m!" psi A m!" t m $ d " 3.38 $ Modulus of elasticity and area of ma member E s!" psi A s!" $ t s $ d s " 7.75 $ Modulus of elasticity of steel and area of two side members E m $ A m R EA!" ".667 u γ s!". $ $ /. E s $ A s 0 E m $ A m E s $ A 3 ".007 s m!" u # u # " $, - m # m n C g!" n$ /&. R EA $ m n ) $ (. m) #. m n ( +, - 4 &, -. R EA $ ' " # m Z'!" C D $ C M $ C t $ C g $ C $ C eg $ C di $ C tn $ Z " lb Adjusted Lateral Design Value P'!" N$ Z' " lb Adjusted allowable force ( ) *+ 4 /6/008 Page 3 of 7 Ver.

8 CE 4, Fall 008 Part (b) Side members: A36 plates, - /4x4 (assumed): l s!" 0.5 t s!" 0.5 F es!" 87000psi d s!" 8 From Table G of NDS: Z!" 390lb γ!" 70000$ & ' ( D ) *+.5 lb $ " $ lb E s!" 9000ksi A s!" $ t s $ d s " 4$ Modulus of elasticity of steel and area of two side members E m $ A m R EA!" " u γ s!". $ $ /. E s $ A s 0 E m $ A m E s $ A 3 ".005 s m!" u # u # " $, - m # m n C g!" n$ /&. R EA $ m n ) $ (. m) #. m n ( + 4 &, -, -. R EA $ ' " 0.96 # m Z'!" C D $ C M $ C t $ C g $ C $ C eg $ C di $ C tn $ Z " lb Adjusted Lateral Design Value P'!" N$ Z' " lb Adjusted allowable force ( Allowable force is higher than previous case, because the design was governed by the side members. Part (c) Length of side members: ) *+ 4 l s D 0.4 " l m D " 5.6.5D " 0.94$ Required edge distance Table.5.A 7$ D " 4.38$ Required end distance Table.5.B 4$ D ".5$ Required bolt spacg Table.5.C There are 4 required end spacgs - at ends and at center!!! There are 4 bolt spacgs. L req!" 4$ ( 7$ D). 4$( 4$ D) " 5.5$ /6/008 Page 4 of 7 Ver.

9 CE 4, Fall 008 Part (d) Allowable tension: P' f t!" " 437.7$ psi Tension stress ma member A m Proceed to calculate the allowable tension the wood with C M " 0.4 Problem 4 This is a standard combed tension and bendg problem. Refer to Example 7.5 on page Forces are: T!" 000lb Tension force & ( ) *+ 3.5 M!" T$ '. " 65 lb$ ft Bendg moment Per problem statement - you will consider only gross section area. A g.5!" Area (gross) S !" Section modulus T f t!" " 63.7$ psi Tensile stress A g M f b!" " $ psi Bendg stress S Check: f f F' t f b. 5.0 F' b Allowable stresses are found as before. /6/008 Page 5 of 7 Ver.

10 CE 4, Fall 008 Problem 5 This is similar to the homework problem 9.4. Part (a) IBC span to width ratio limit is 3: Part (b) 0ft 60ft ".83 OK Note that earthquake governs longitudal direction and wd governs transverse direction sce: L W!" 0ft B!" 60ft Longitudal and transverse dimensions!" 350plf Wd load E lon!" 0.7$ 660plf " 46$ plf E tra!" 0.7$ 360plf " 5$ plf Earthquake load B v lon!" E lon $ $ " 6$ plf Diaphragm shear for longitudal direction L v tra W L!" $ $ " 30.83$ plf Diaphragm shear for transverse direction B Go to IBC Tables and select required plywood thickness, grade, nailg and blockg (if required). Draw a plywood shear diagram (shear will be zero at the center and learly creasg towards the ends) and see which region (if any) can nailg be reduced, i.e. from 4" on center to 6" on center. It is recommended to use not more than -3 different nail spacgs (IBC Tables provide 4 different spacgs). This is diaphragm Case. Part (c) Aga, draw a plywood shear diagram (shear will be zero at the center and learly creasg towards the ends) and see which region (if any) can blockg be omitted. You do this by comparg the shear with the allowable shear for unblocked case. Part (d) Cord forces are: WL $ P!" $ " 88.9 lb Force the transverse cords (short side) 8 B E lon $ B P!" $ " 890 lb Force the longitudal cords (long side) 8 L /6/008 Page 6 of 7 Ver.

11 CE 4, Fall 008 Part (e) Shear flows are: L A!" 0ft L B!" B " 60 ft Length of walls WL $ q A!" $ " 96.5 $ plf Shear flow wall A L A WL $ q B!" $ " 30.83$ plf Shear flow wall B L B Part (f) Collector forces are obtaed plottg the diagrams as the homework problem 9.4 or Example 9. on page /6/008 Page 7 of 7 Ver.