Calculation and experimental check of a nailing schedule for conventional roof frames

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Calculation and experimental check of a nailing schedule for conventional roof frames

NATIONAL I?3SEARCH COUNCIL CANADA

D I V I S I O N O F B U I L D I N G lXESEARCH

CALCULATION AND EXPERIIVlEN!I!AL CHECK O F A N A I L I N G SCKEDULE F O R CONVENT1 ONAL ROOF FRAIJES

by H , J, Thorburn I n t e r n a l R e p o r t N o . 263 o f the D i v i s i o n of B u i l d i n g R e s e a r c h OTTAWA June

1963

PREFACE

The D i v i s i o n of B u i l d i n g Research h a s f o r some time s t u d i e d t h e s t r u c t u r a l performance of house r o o f s . During t h e s t u d y , which embraced c o n v e n t i o n a l ( r a f t e r and j o i s t ) frames a s w e l l a s t r u s s e s , it became a p p a r e n t t h a t u n t i l r e c e n t l y code r e q u i r e m e n t s f o r c o n v e n t i o n a l r a f t e r and j o i s t r o o f s d i d n o t always e n s u r e adequate l o a d - b e a r i n g c a p a c i t i e s . Laboratory t e s t s show t h a t many c o n v e n t i o n a l r o o f s l a c k

adequate n a i l i n g t o develop a r e a s o n a b l e margin of s a f e t y . The purpose of t h i s r e p o r t i s t o o u t l i n e t h e back- ground of t h e p r e s e n t s i t u a t i o n and t o c o n s i d e r some of t h e main improvements r e q u i r e d i n t h e n a i l i n g t o b r i n g t h e s t r e n g t h

of t h e n a i l e d c o n n e c t i o n s c l o s e r t o t h e d e g r e e of r e f i n e m e n t reached i n "span t a b l e s . " T h i s r e p o r t p r e s e n t s a s e r i e s of

" n a i l i n g t a b l e s " , based on c a l c u l a t i o n s and e x p e r i m e n t a l checks, which would b r i n g t h e s t r e n g t h of r a f t e r and j o i s t r o o f frames up t o t h e s t r e n g t h p r e s e n t l y r e q u i r e d i n t r u s s e s . T h i s r e p o r t concludes w i t h some comments on t h e d i f f i c u l t q u e s t i o n of what margin of s a f e t y should be r e q u i r e d i n c o n v e n t i o n a l house r o o f s .

The a u t h o r of t h i s r e p o r t was a r e s e a r c h o f f i c e r w i t h t h e B u i l d i n g S t r u c t u r e s S e c t i o n of t h e D i v i s i o n , who l e f t t o t a k e up g r a d u a t e s t u d i e s a t t h e U n i v e r s i t y of B r i s t o l on a n Athlone Fellowship. Vhile a t t h e D i v i s i o n he a l s o worked on t h e s t u d y of snow l o a d s on r o o f s , a p r o j e c t which h a s con- s i d e r a b l e b e a r i n g on t h e s u b j e c t covered i n t h i s r e p o r t .

Ottawa

June 1963

N.

B. Hutcheon

CALCULATION AND EXPERIAIENTAL CHECK OF A N A I L I N G SCHEDULE FOR CONVENTIONAL ROOF FRAMES

H. J . Thorburn

I n view of t h e importance of snow l o a d s i n Canada, codes and s t a n d a r d s of d w e l l i n g c o n s t r u c t i o n have c o n t a i n e d r e g u l a t i o n s governing roof framing s i n c e e a r l y i n t h e i r development. Perhaps t y p i c a l of e a r l i e r codes a r e t h e r e g u l a t i o n s of t h e 1941 e d i t i o n of t h e N a t i o n a l B u i l d i n g Code which s t a t e d i n p a r t :

"The span of any r a f t e r o r roof j o i s t s h a l l be such t h a t t h e a l l o w a b l e f i b r e s t r e s s e s w i l l n o t be exceeded when t h e l o a d s p r e s c r i b e d i n . .

. . .

a r e a p p l i e d . " The c l a u s e continued by s t a t i n g t h a t f o r d w e l l i n g s , t h e s e r e q u i r e m e n t s would be c o n s i d e r e d met i f spans l i s t e d i n a t a b l e which r e l a t e d s p e c i e s , nominal dimensions, s p a c i n g and

spans were used. These spans were based on t h e mentioned

a l l o w a b l e f i b r e s t r e s s e s b u t d i s r e g a r d e d v a r y i n g l o a d s s i n c e t h e y were a l l based on 40 p s f . Por t h e c o n n e c t i o n s o r n a i l i n g between t h e roof framing members t h e 1941 code d i d n o t c o n t a i n any s p e c i f i c reqbirements,but i n a g e n e r a l c l a u s e s t a t e d :

" A l l members s h a l l be s o anchored, t i e d and braced t o g e t h e r a s t o develop t h e s t r e n g t h and r i g i d i t y n e c e s s a r y f o r t h e purpose f o r which t h e y a r e used.

Compliance w i t h t h i s c l a u s e was a s s i s t e d by t h e s p e c i f y i n g of t h e a l l o w a b l e l o a d s on v a r i o u s f a s t e n i n g s i n c l u d i n g common wire n a i l s .

The r e q u i r e m e n t s f o r d w e l l i n g roof framing remained i n e s s e n t i a l l y t h i s form u n t i l 1950 when t h e C e n t r a l Mortgage and Housing Corporation i s s u e d a r e v i s i o n of i t s " B u i l d i n g S t a n d a r d s . " A s b e f o r e , t h e a l l o w a b l e spans were s e t o u t i n a t a b l e r e l a t i n g s p e c i e s , nominal dimensions, spacing and

spans f o r l o a d s of 40 p s f . For t h e c o n n e c t i o n s , however, t h e r e was a new requirement:

" N a i l i n g of s p e c i f i c j o i n t s i n wood f r a m i n g s h a l l conform t o t h e f o l l o w i n g u s i n g common o r smooth box n a i l s . . . C e i l i n g j o i s t s , t o p l a t e ( t o e n a i l ) 2-34" n a i l s l a p s o v e r p a r t i t i o n s 3-3?" n a i l s t o p a r a l l e l a l t e r n a t e r a f t e r s 3-3711 n a i l s R a f t e r t o p l a t e 3-321' n a i l s

...,...

Other j o i n t s

...

11

This n a i l i n g was applioablet t o t h e framing of a l l r o o f s r e g a r d - l e s s of span o r s l o p e , and, l i k e t h e span t a b l e , r e g a r d l e s s of varying l o a d s .

The span t a b l e and n a i l i n g schedule of t h e "Building Standardst1 remained b a s i c a l l y unchanged when t h e y became p a r t of t h e 1953 e d i t i o n of t h e National Building Code, except f o r

one s i g n i f i c a n t p o i n t . Although t h e t a b l e of allowable spans was s t i l l based on a load of 40 psf only,

i t was accompanied

by a statement which allowed f o r o t h e r l o a d s by adjustment of t h e frame spacing. Although t h i s was a n improvement, notwith- s t a n d i n g t h e f a c t t h a t

it

reduced t h e freedom of choice of spacing,

it

d i d n o t appear i n t h e QbIHC "Building Standards" of t h a t time nor i n i t s s u c c e s s o r , "Housing Standards," i s s u e d by t h e D i v i s i o n of Building Research i n 1958. The n a i l i n g schedule remained unchanged i n a l l t h r e e r e g u l a t i o n s .

A f u r t h e r s t e ~ i n t h e d e v e l o ~ m e n t of t h e m a n t a b l e and n a i l i n g schedule h a s r e c e n t l y b e e n A p u t i n t o p r a c t i c e by t h e Housing Standards, Canada, 1963 (Supplement No.

5

t o t h e 1960 e d i t i o n of t h e National Building c o d e ) . The span t a b l e s

(Appendix A ) have been g r e a t l y enlarged and now c o n t a i n s e p a r a t e t a b l e s f o r a number of d i f f e r e n t wood s p e c i e s and snow l o a d s

(30, 40 o r 50 _{p s f ) . Within each t a b l e t h e allowable span i s} f u r t h e r r e l a t e d t o t h e grade of lumber, t h e nominal dimensions and t h e spacing of members. Thus, t h e s e l e c t i o n of spans h a s been c o n s i d e r a b l y r e f i n e d . I n t h e s e l e c t i o n of t h e r e q u i r e d n a i l i n g c o n s i d e r a b l e refinement has a l s o been made. There i s now a schedule of n a i l i n g f o r t h e main connections i n roof frames i n which t h e number of n a i l s r e q u i r e d h a s been r e l a t e d t o s e l e c t e d roof s l o p e s , frame s p a c i n g s , ranges of roof span

(Table XX of t h e Housing S t a n d a r d s ) and t h r e e snow load zones. I n o r d e r t o achieve balance i n s t r e n g t h between members and connections a n equal degree of refinement i n t h e span t a b l e s and t h e n a i l i n g t a b l e i s d e s i r a b l e s i n c e t h e r e

i s l i t t l e p o i n t i n having members t h a t w i l l c a r r y more l o a d than t h e connections o r v i c e v e r s a u n l e s s , of c o u r s e , f a c t o r s o t h e r t h a n s t r e n g t h govern. Furthermore, equal degrees of refinement a r e d e s i r a b l e i n view o f t h e need f o r a r a t i o n a l engineering approach t o roof-frame d e s i g n which r e s u l t s from t h e t r e n d t o performance-type codes, r a t h e r t h a n s p e c i f i c a l i o n - type codes.

I t i s t h e purpose of t h i s r e p o r t t o c o n s i d e r some

o f t h e changes r e q u i r e d i n t h e n a i l i n g schedule t o b r i n g it

c l o s e r t o t h e degree of refinement o f t h e span t a b l e s . Bases f o r t h e s e changes a r e s e t out and c a l c u l a t i o n s of t h e r e q u i r e - ments a r e made. The r e p o r t t h e n d e s c r i b e s t h e experimental work c a r r i e d out t o check t h e c a l c u l a t i o n s and concludes w i t h comnents on t h e p r a c t i c a l a p p l i c a b i l i t y of t h e c a l c u l a t e d values.

CALCULATION OF N A I L I N G SCHEDULE Broadly, t h e approach t a k e n i n t h e c a l c u l a t i o n of t h e n a i l i n g s c h e d u l e amounts t o a n " u l t i m a t e l o a d f t d e s i g n . A f t e r t h e b a s e s f o r t h e c a l c u l a t i o n s were e s t a b l i s h e d , t h e d e s i r e d "design l o a d s " were m u l t i p l i e d by a l o a d f a c t o r t o d e t e r n i n e u l t i m a t e o r f a i l u r e l o a d s . The number of n a i l s r e q u i r e d t o r e s i s t t h e s e l o a d s was t h e n c a l c u l a t e d u s i n g u l t i m a t e n a i l s t r e n g t h s . Bases of C a l c u l a t i o n I n e s t a b l i s h i n g t h e b a s e s f o r t h e c a l c u l a t i o n s t h e r e q u i r e m e n t s of t h e s p a n t a b l e s and t h e n a i l i n g schedule

i n

t h e Housing S t a n d a r d s were c o n s i d e r e d . From t h e s e two g u i d e s t h e f o l l o w i n g b a s e s of c a l c u l a t i o n were e s t a b l i s h e d : Loads The s p a n t a b l e s s e t . t h e p r e c e d e n t f o r l o a d s by c o n s i d e r i n g 50-psf l i v e l o a d + 6 - p s f dead l o a d 40-psf l i v e l o a d

+

6 - p s f dead l o a d 30-psf l i v e l o a d + 6-psf dead l o a d Although t h e r e a r e of c o u r s e o t h e r d e s i g n l o a d v a l u e s , t h e r e i s l i t t l e p o i n t i n having t h e n a i l i n g schedule d i f f e r e n t from t h e span t a b l e s . The above v a l u e s , reduced by t h e snow l o a d s l o p e - r e d u c t i o n f a c t o r i n c a l c u l a t i n g t h e t h r u s t f o r frames w i t h s l o p e s g r e a t e r t h a n 30 deg, were t h e r e f o r e used i n t h e

c a l c u l a t i o n s . The span t a b l e s a l s o s e t t h e c e i l i n g l o a d , t o be c o n s i d e r e d a t 4 p s f .

Frame s ~ a c in^

The span t a b l e s a r e based on member s p a c i n g s of 1 2 , 1 6 , 20 and 24 i n . O . C . and t h e Housing S t a n d a r d s ' n a i l i n g

t a b l e s on member s p a c i n g s of 1 6 and 24 i n . O . C . A s a com-

promise and i n view of t h e f a c t t h a t t h e 20-in. s p a c i n g i s n o t a modular dimension ( r e l a t i v e t o 4-by 8 - f t s h e e t s of c o v e r i n g m a t e r i a l ) t h e 20-in. s p a c i n g i s d i s r e g a r d e d i n t h i s r e p o r t , l e a v i n g 1 2 , 16 and 24

i n .

Roof s l o p e s

The Housing S t a n d a r d s ' n a i l i n g s c h e d u l e s e t s t h e p r e c e d e n t f o r s l o p e s by u s i n g

For purposes of t h i s r e p o r t , it i s considered s u f f i c i e n t t o use t h e above, I t might be mentioned t h a t f o r lower s l o p e s r i d g e support i s r e q u i r e d ( e x c e p t when t r u s s e s a r e u s e d ) , i n which case t h e n a i l i n g between j o i s t s and r a f t e r s i s reduced

t o 3 n a i l s because t h e h o r i z o n t a l r a f t e r t h r u s t i s e l i m i n a t e d . Roof m a n s

The Housing Standards' n a i l i n g schedule a l s o s e t s

a

precedent f o r t h e roof spans t o be considered i n t h e c a l c u l a - t i o n s by u s i n g ranges of "house width up t o 26 f t n and "house width up t o 32 f t . " There seemed t o be some m e r i t , however, i n c o n s i d e r i n g o t h e r r a n g e s , because f i r s t , t h e s e increments of range a r e f a i r l y l a r g e , second,

i t would be u s e f u l t o have

a n i d e a of t h e v a r i a t i o n of n a i l i n g w i t h span and t h i r d , some load t e s t s have a l r e a d y been done on spans of 24 f t , I t was t h e n decided t o use roof spans of 1 6 , 20, 24, 28 and 32 f t i n t h e c a l c u l a t i o n s ,

Size of n a i l s

Although t h e Housing Standards' n a i l i n g schedule i n i t s f i n a l Sorm r e q u i r e s 3&-in. n a i l s , t h e c a l c u l a t i o n s were based on 32-in. n a i l s . This was n e c e s s a r y because 33-in.

n a i l s had been used i n t h e frame t e s t s from which t h e u l t i m a t e n a i l s t r e n g t h s used i n t h e c a l c u l a t i o n s were determined, N a i l

l e n g t h s of 33 i n , had been used i n t h e s e t e s t s because t h e Housing Standards' n a i l i n g schedule a s f i r s t considered and t h e n a i l i n g schedule i n t h e old Housing Standards 1958 had both r e q u i r e d 34-in. n a i l s .

There a r e s e v e r a l assumptions t o be made i n t h e c a l c u l a t i o n s f o r which t h e r e i s no precedent i n t h e span t a b l e s o r t h e Housing Standards' n a i l i n g schedule and f o r which, t h e r e f o r e , o t h e r c o n s i d e r a t i o n s must govern.

T Y D ~ of roof frame

The type of roof frame assumed i n t h e c a l c u l a t i o n s should be of t h e type most widely used. Since

it appears t h a t

sloped r o o f s a r e most commonly e i t h e r gable o r h i p r o o f s , t h e frame t o c o n s i d e r would seem t o be one w i t h t h e o v e r - a l l shape of a n i s o s c e l e s t r i a n g l e . S e v e r a l arrangements of secondary members w i t h i n t h i s shape a r e i n common u s e ; t h e i r s t r u c t u r a l a c t i o n s a r e d i f f e r e n t b u t which of t h e s e should be considered

i s n o t r e a d i l y apparent. It would seem l o g i c a l t o assume, however, t h a t t h e arrangement which produces t h e most s e v e r e c o n d i t i o n s a t t h e j o i n t s d e a l t with by t h e n a i l i n g t a b l e should be considered. Accordingly, a f t e r c a l c u l a t i o n s showed t h a t of t h e f o u r common arrangements (simple, diagonal b r a c e , dwarf w a l l , and c o l l a r - t i e ) t h e c o l l a r - t i e d frame produced

t h e g r e a t e s t f o r c e s a t t h e j o i n t s under a g i v e n uniform r o o f l o a d , t h i s frame was used a s a b a s i s f o r c a l c u l a t i n g t h e n a i l i n g schedule ( F i g u r e 1).

Support c o n d i t i o n s

Since b o t h t h e c a l c u l a t i o n and t e s t i n g of t h e n a i l i n g a r e i n f l u e n c e d by t h e manner i n which t h e roof frames a r e

su2ported a t t h e i r e n d s , some assumption had t o be made of t h i s . A c t u a l c o n d i t i o n s probably v a r y from a l m o s t completely f i x e d t o almost completely f r e e , w i t h many c a s e s i n p r a c t i c e probably b e i n g n e a r e r t o t h e "completely f r e e " c o n d i t i o n . Simulating a n Itin between c o n d i t i o n " s o t h a t it might be a

known q u a n t i t y would have been d i f f i c u l t , however. It was d e c i d e d , t h e r e f o r e , t o assume t h e most s e v e r e c o n d i t i o n and c o n s i d e r t h e frames t o be completely f r e e , i . e . t h e c a s e approached by a roof r e s t i n g on l o n g l a t e r a l l y unsupported w a l l s such a s o v e r a l a r g e l i v i n g room.

Load f a c t o r

The c h o i c e of a l o a d f a c t o r by which t o i n c r e a s e t h e working l o a d s t o determine t h e u l t i m a t e l o a d s i n v o l v e s many c o n s i d e r a t i o n s . To determine a f a c t o r from fundamental c o n s i d e r a t i o n s i s n o t t h e i n t e n t of t h i s r e p o r t ; t h e c h o i c e must be made on t h e b a s i s of p r e c e d e n t and e x p e r i e n c e . I n t h i s r e g a r d t h e span t a b l e s o f f e r l i t t l e guidance because t h e y were determined on a n a l l o w a b l e s t r e s s b a s i s . ( T h i s may imply a f a c t o r of a b o u t 3 t o

5 ,

b u t such a f a c t o r a p p l i e d t o t h e n a i l i n g would n o t l e a d t o a balance between j o i n t and member s t r e n g t h . ) Some guidance can be o b t a i n e d from a

p r e c e d e n t e s t a b l i s h e d i n t h e a c c e p t a n c e of l i g h t wooden

W-trusses f o r house r o o f s . I n t h i s c a s e a l o a d f a c t o r of 2 ,

a p p l i e d t o t h e l i v e l o a d s o n l y , was chosen. The b a s i s f o r t h e choice of t h i s v a l u e , which r e s t s mainly on c o n s i d e r a t i o n s of t h e s t r e n g t h of e x i s t i n g c o n v e n t i o n a l r o o f s and t h e snow l o a d s a c t i n g on them, h a s been e x p l a i n e d elsewhere. Although one could a r g u e whether t h i s l o a d f a c t o r of 2 should now be a p p l i e d t o t h e n a i l i n g of c o n v e n t i o n a l roof frames, it would seem

l o g i c a l t o adopt it a s a f i r s t s t e p . Thus t h e b a s i c u l t i m a t e l o a d s f o r which numbers of n a i l s must be determined a r e :

( 2 x 5 0 ) + 6 = 106 p s f ( 2

x

40) +

₆

= 86 psf ( 2

x

30) + 6 = 66 p s f

The c o n n e c t i o n s f o r which c a l c u l a t i o n s should be made a s i n d i c a t e d by t h e Housing S t a n d a r d s ' n a i l i n g s c h e d u l e , a r e t h e h e e l j o i n t and t h e c e i l i n g j o i s t s p l i c e . However, s i n c e

it

i s p o s s i b l e on t h e b a s i s of e a r l i e r t e s t r e s u l t s (1) t o r e l a t e t h e s p l i c e n a i l i n g t o t h e h e e l j o i n t n a i l i n g by a simple r u l e , a c t u a l c a l c u l a t i o n s a r e r e q u i r e d f o r t h e h e e l

j o i n t n a i l i n g o n l y . I d e a l l y , t h e n a i l i n g a t s e c o n d a r y connec- t i o n s s u c h a s t h e c o l l a r - r a f t e r j o i n t s h o u l d a l s o be s c h e d u l e d b u t t h i s i s _{beyond t h e i n t e n t of t h e p r e s e n t work.} C a l c u l a t i o n s B r i e f l y o u t l i n e d , t h e method of c a l c u l a t i o n c o n s i s t e d of e s t a b l i s h i n g a r e l a t i o n s h i p between t h e u n i f o r m l o a d on

t h e frame and t h e f o r c e s a t t h e , n a i l e d c o n n e c t i o n s and r e l a t i n g t h e s e f o r c e s t o t h e numbers and s t r e n g t h of n a i l s a t t h e c o n n e c t i o n s . The u n i f o r m l o a d s on t h e f r a m e s were d e t e r m i n e d by a d j u s t i n g , accordin:? t o t h e frame s p a c i n ~ , t h e v a l u e s of t h e d e s i g n l o a d s i n c r e a s e d by t h e l o a d f a c t o r , Values f o r t h e f a i l u r e s t r e n g t h s of n a i l s were d e t e r m i n e d by a p p l y i n g t h e r e l a t i o n s h i p s " i n r e v e r s e " t o some p r e v i o u s l y t e s t e d r o o f f r a m e s f o r which t h e f a i l u r e l o a d s and number o f n a i l s were known. These n a i l s t r e n g t h s were then. used t o d e t e r m i n e t h e number of n a i l s needed t o g i v e t h e r e q u i r e d u l t i m a t e frame s t r e n g t h s .

The r e s u l t s of -the c a l c u l a t i o n s a r e shown i n T a b l e s I , I1 and I11 where f o r e a c h d e s i g n r o o f load. t h e n a i l i n g i s

r e l a t e d t o t h e r o o f s p a n , s l o p e and frame s p a c i n g . The numbers i n t h e s e t a b l e s have g e n e r a l l y b e e n rounded up. EX.I?ERIl.IEBTAL CHECKING OF TJAILIMG SCHEDUL-E

To o b t a i n some i d e a of tile r e l i a b i l i t y of t h e c a l c u l a t i o n s made i n e s t a b l i s h i n g t h e n a i l i n g s c h e d u l e , i t

w a s t h o u g h t t h a t sone e x p e r i m e n t a l c h e c k i n 6 s h o u l d be c a r r i e d o u t , t h e p r i m a r y i n t e n t i o n b e i n g t o examine f a i l u r e l o a d s .

It d i d n o t seem n e c e s s a r y n o r would i t have b e e n p r a c t i c a l t o t e s t e a c h of t h e 270 c o m b i n a t i o n s of f a c t o r s : t h e f o l l o w i n g f r a m e s which were c o n s i d e r e d r e p r e s e n t a t i v e of t h o s e i n

c u r r e n t u s e ~ v e r e th e r e f o r e s e l e c t e d :

Spans S l o p e s Loads and S p a c i n g s 24 f t 4 i n 1 2 40 psf 1 2 i n . O . C . 28 f t 5 i n 1 2 50 psf 1 6 i n . O . C . 6 i n 1 2

50

p s f 24 i n , O . C .

9

_{i n 1 2} T h i s r e p r e s e n t e d 2 4 c o m b i n a t i o n s t o be c o n s i d e r e d , b u t s i n c e t h o s e w i t h a 2 4 - f t s p a n and

5

i n 1 2 s l o p e had b e e n t e s t e d p r e v i o u s l y ( l ) , o n l y 2 1 had t o be t e s t e d . T h i s s e l e c t i o n o f f r a m e s a c t u a l l y a l l o w e d more t h a n 2 1 c h e c k s on t h e c a l c i ~ l a t i o n s s i n c e f o r a n y one c o m b i n a t i o n o f span and s l o p e , t h e t e s t s

made f o r t h e t h r e e l o a d - s p a c i n g c o m b i n a t i o n s i n d i c a t e d a r e l a t i o n s h i p be tween f a i l u r e l o a d and number o f n a i l s b y which o t h e r l o a d - s p a c i n g c o m b i n a t i o n s c o u l d be checked b y i n t e r p o l a t i o n and e x t r a p o l a t i o n .

T e s t S t r u c t u r e s

B a s i c a l l y , t h e t e s t e d r o o f f r a m e s were b u i l t a c c o r d i n g t o t h e r e q u i r e m e n t s of t h e Housing S t a n d a r d s . R a f t e r and j o i s t s i z e s were determined from t h e span t a b l e s a c c o r d i n g t o lumber s p e c i e s and g r a d e , d e s i g n l o a d and frame s p a c i n g . The main n a i l i n g of t h e frames ( i . e . t h r o u g h n a i l i n g a t h e e l j o i n t and

j o i s t s p l i c e ) was a s c a l c u l a t e d f o r t h e n a i l i n g s c h e d u l e . Although secondary c o n n e c t i o n s were n o t i n c l u d e d i n t h e

c a l c u l a t i o n s , t h e n a i l i n g of t h e c o l l a r - t i e t o t h e r a f t e r i n t h e t e s t frames was s e l e c t e d t o match t h e main n a i l i n g . Toe- n a i l i n g was v a r i e d s l i h t l y from t h e Housing S t a n d a r d s '

_?

r e q u i r e m e n t of t h r e e 38-in. n a i l s r a f t e r t o p l a t e and two 3?-in. n a i l s j o i s t t o p l a t e , i n t h a t 3 & - i n . n a i l s were used. Grade-marked No. 1 ( C o n s t r u c t i o n ) E a s t e r n Spruce which v a r i e d i n m o i s t u r e c o n t e n t from

1 5

t o 20 p e r c e n t i n i t i a l l y down t o 6 t o

7

p e r c e n t f o r most of t h e t e s t was used f o r a l l members. ' T e s t Arrangement

Each of t h e 2 1 r o o f frames was t e s t e d s i n g l y i n a l o a d i n g r i g whi-ch c o n s i s t e d of e i g h t l o a d i n g booms ( l e v e r a r m s ) e a c h pin-connected t o a v e r t i c a l s u p p o r t a t one end, b e a r i n g on t h e r a f t e r of t h e r o o f frame a t t h e o t h e r and l o a d e d t o mid-span by a h y d r a u l i c p u l l jack ( F i g u r e

3 ) .

Half of t h e downward p u l l of t h e jack was t h u s a p p l i e d t o t h e r a f t e r by t h e booms, e a c h boom l o a d s i m u l a t i n g t h e uniform l o a d on one e i g h t h of t h e span ( T i e r e 2 ) . The

l o a d i n g booms were l o c a t e d a t d i f f e r e n t h e i g h t s c o r r e s p o n d i n g t o t h e s l o p e of t h e r a f t e r s and were k e p t a p p r o x i m a t e l y

h o r i z o n t a l d u r i n g t e s t i n g .

Wooden wedges of t h e same a n g l e a s t h e r o o f s l o p e were p l a c e d between t h e booms and t h e r a f t e r s t o p r o v i d e h o r i z o n t a l b e a r i n g s u r f a c e s . B e s i d e s l o a d i n g t h e f r a m e s , t h e booms provided l a t e r a l b r a c i n g f o r t h e r a f t e r s by means of wooden b l o c k s which extended from t h e booms and s t r a d d l e d t h e r a f t e r s . Also p a r t of t h e l o a d i n g r i g were f o u r members which p a r a l l e l e d t h e l o a d i n g booms and were e a c h pinned a t

one end t o t h e l o a d i n g r i g . Three of t h e s e members a c t e d a s p a r t of t h e double w a l l p l a t e s a t t h e s u p ~ o r t s and provided t h e moment r e q u i r e d t o r e s i s t t h e c o u p l e a p p l i e d t o t h e p l a t e by t h e e c c e n t r i c h e e l j o i n t o r j o i s t s p l i c e . The f o u r t h

member provided l a t e r a l b r a c i n g f o r t h e mid-span of t h e c o l l a r s t r u t .

Support f o r t h e frames was provided a t t h r e e p o i n t s .

A t one h e e l j o i n t f r i c t i o n between t h e w a l l p l a t e and t h e

s u p p o r t i n g c o n c r e t e b l o c k s h e l d t h e j o i n t i n a f i x e d p o s i t i o n . The p l a t e of t h e o t h e r h e e l j o i n t was mounted on r o l l e r s on t h e c o n c r e t e b l o c k s and was f r e e t o move i n t h e h o r i z o n t a l d i r e c t i o n p a r a l l e l t o t h e frame. The t h i r d s u p p o r t , a l s o a r o l l e r s u p p o r t , was provided a t t h e j o i s t s p l i c e ( F i g u r e 1 ) .

The r o o f l o a d a p p l i e d t o t h e f r a m e s was governed by a pump-dynamometer combination which f e d o i l p r e s s u r e through a common l i n e t o t h e e i g h t jacks. A p r e v i o u s c a l i b r a t i o n enabled r o o f l o a d s t o be determined from o i l p r e s s u r e s .

C e i l i n g l o a d , on t h e o t h e r hand, r e q u i r e d no v a r i a t i o n d u r i n g any one t e s t and was t h e r e f o r e a p p l i e d by means of l e a d s h o t - f i l l e d bags p i l e d a l o n g t h e j o i s t s .

D e f l e c t i o n s of t h e f r a m e s under l o a d were measured i n s e v e r a l ways a t s e v e r a l p o i n t s . The s p r e a d of t h e e x t e r i o r w a l l p l a t e s which comprised t h e movements a t b o t h h e e l j o i n t s and t h e j o i s t s p l i c e was measured by means of t h e e q u i v a l e n t of a t e l e s c o p i n g r o d l i n k e d between p l a t e s and h a v i n g a s c a l e a t i t s mid-length t o i n d i c a t e t h e amount of e x t e n s i o n . B y

s u b t r a c t i n g t h e v a l u e of t h e s l i p a t t h e j o i s t s p l i c e (which was measured by a s c a l e on one s i d e of t h e s p l i c e r e a d

r e l a t i v e t o a l i n e on t h e o t h e r s i d e ) from t h e v a l u e of t h e e x t e n s i o n of t h e t e l e s c o p i n g r o d , t h e n e t movements of t h e h e e l j o i n t s were determined. V e r t i c a l movement of t h e r i d g e was i n d i c a t e d on a s c a l e by a weight hanging on a w i r e from t h e r i d g e . The d e f l e c t i o n of t h e r a f t e r s was measured by means of a t a u t w i r e r u n n i n g from r i d g e t o h e e l , t h e movement of t h e mid-span of t h e r a f t e r p e r p e n d i c u l a r t o t h e wire b e i n g t h e d e f l e c t i o n of t h e r a f t e r r e l a t i v e t o i t s ends.

T e s t Procedure

A f t e r each frame had been b u i l t i n p l a c e i n t h e l o a d i n g r i g and t h e d e f l e c t i o n measuring a p p a r a t u s i n s t a l l e d , t h e l o a d i n g procedure began w i t h t h e a p p l i c a t i o n of t h e c e i l i n g l o a d t o t h e j o i s t s . A "bedding-in" l o a d of h a l f t h e d e s i g n l i v e l o a d was t h e n a p p l i e d t o t h e r a f t e r s f o r

5

min and removed. A f t e r a 5-min r e c o v e r y p e r i o d " z e r o " d e f l e c t i o n r e a d i n g s were t a k e n . The f i r s t c y c l e of t e s t l o a d was t h e n a p p l i e d i n 1 0 - l b / f t i n c r e m e n t s , each i n c r e m e n t b e i n g a p p l i e d i n 1 rnin and h e l d f o r

5

min until t h e f u l l d e s i g n l i v e l o a d was reached. The l o a d was t h e n removed,

5

min allowed f o r r e c o v e r y , and "zero't d e f l e c t i o n r e a d i n g s t a k e n a g a i n . F i n a l l y , t h e frames were loaded t o f a i l u r e i n a c y c l e of l o a d w i t h t h e same s i z e increment a p p l i e d a t t h e same r a t e a s i n t h e f i r s t c y c l e . D e f l e c t i o n r e a d i n g s were talcen a f t e r e a c h increment of l o a d i n a d d i t i o n t o t h e " z e r o " r e a d i n g s .

I n t h e few c a s e s where f a i l u r e o c c u r r e d f i r s t a t t h e j o i s t s p l i c e o r t h e c o l l a r - r a f t e r c o n n e c t i o n , t h e

j o i n t was r e p a i r e d and t h e frame l o a d e d a g a i n t o f a i l u r e . T h i s l o a d i n s was a p p l i e d w i t h o u t i n c r e m e n t s b u t a t t h e same l o a d a p p l i c a t i o n r a t e a s t h e o t h e r c y c l e s , 1 0 l b / f t / m i n . No d e f l e c t i o n r e a d i n g s were t a k e n .

T e s t R e s u l t s

O v e r - a l l , t h e t e s t r e s u l t s a r e i n f a i r l y good a g r e e - ment w i t h t h e c a l c u l a t e d f a i l u r e l o a d s a s c a n be s e e n from t h e summary of t e s t r e s u l t s g i v e n i n Table I V . Although i n a few c a s e s t h e v a r i a t i o n s of t h e t e s t r e s u l t s from t h e c a l c u l a t e d l o a d s were l a r g e ( u p t o 20 p e r c e n t , a v a l u e n o t unexpected i n t e s t s on n a i l e d wooden s t r u c t u r e s ) , t h e a v e r a g e v a r i a t i o n was o n l y 8 p e r c e n t . More s i g n i f i c a n t i s t h e f a c t t h a t t h e d i s t r i b u t i o n of t h e v a r i a t i o n s i s a p p r o x i m a t e l y

s y m m e t r i c a l , ;vith n e a r l y t h e same number of t e s t r e s u l t s above t h e c a l c u l a t e d l o a d s a s below.

Although t h e c a l c u l a t i o n of t h e n a i l i n g was made on a s t r e n g t h b a s i s , d e f l e c t i o n s were a l s o of i m p o r t a n c e and

c o n s i d e r a b l e c a r e was talcen t o o b s e r v e them. Ridge d e f l e c t i o n s , f o r example, v a r i e d f r o n a p p r o x i m a t e l y 1/16 i n . f o r f r a m e s w i t h 9 i n 12 s l o p e s and 24-f-t s p a n s , up t o 3/8 i n . f o r f r a m e s w i t h 4 i n 1 2 s l o p e s and 2 8 - f t s p a n s , t h e s e v a l u e s b e i n g observed a t f u l l d e s i g n l i v e l o a d . R a f t e r mid-span d e f l e c t i o n s i n c r e a s e d w i t h d e c r e a s i n g s l o p e b u t showed no i n f l u e n c e of s p a n . T h e i r v a l u e s a t f u l l d e s i g n l i v e l o a d were i n t h e r a n g e 1/6 t o 1/4 i n . The d i s p l a c e m e n t s measured a t t h e j o i s t s p l i c e and a t t h e w a l l p l a t e s d i d n o t f o l l o w a n a p p a r e n t o r d e r , b u t were c o n s i s t e n t l y s m a l l a t v a l u e s of t h e o r d e r of 1/32 and 1/8 i n . r e s p e c t i v e l y . The r e s i d u a l d e f l e c t i o n s o r s e t s a f t e r removal o f t h e l o a d a r e a l s o o f i n t e r e s t . Expressed i n t h e u s u a l manner a s a p e r c e n t a g e of t h e d e f l e c t i o n o r d i s p l a c e m e n t u n d e r l o a d , t h e s e t s a r e q u i t e v a r i a b l e , r a n g i n g from n e g l i g i b l e t o 1 0 0 p e r c e n t ( r a f t e r mid-spans and j o i s t s p l i c e s r e s p e c t i v e l y ) . Most, however, were i n t h e 20 t o 40 p e r c e n t r a n g e . Expressed a s a b s o l u t e v a l u e s t h e s e t s do n o t a p p e a r v e r y l a r g e . They were g e n e r a l l y of t h e o r d e r of 1/32 i n . t o l e s s t h a n 1/16 i n . , t h e l a r g e s t o c c u r r i n g a t t h e r i d g e and w a l l p l a t e . One n o t a b l e f e a t u r e of t h e r e s u l t s i s t h e f a c t t h a t i n none of t h e t e s t s d i d f a i l u r e o c c u r i n a member.

INTERIPRETATIOB OF TEST mSULTS

The g e n e r a l agreement between t h e t e s t r e s u l t s and t h e c a l c u l a t e d performance i n d i c a t e s t h a t t h e c a l c u l a t e d n a i l i n g was a d e q u a t e f o r p r o v i d i n g t h e p r e d i c t e d s t r e n g t h s ; t h i s would s u g g e s t t h a t t h e a p p r o a c h t a k e n i n t h e c a l c u l a t i o n of t h e n a i l i n g i s f u n d a m e n t a l l y c o r r e c t . It seems s a f e t o assume t h e r e f o r e t h a t t h e u n t e s t e d f r a m e s a l s o had t h e c a l c u l a t e d s t r e n g t h .

It would seem t h a t t h e g e n e r a l l y s m a l l d e f l e c t i o n s observed a t t h e f u l l d e s i g n l i v e l o a d s a r e w e l l w i t h i n

r e a s o n a b l e l i m i t s and a c c e p t a b l e f o r purposes ot' t h e n a i l i n g s c h e d u l e .

The t e s t r e s u l t s confirmed t h e r u l e which was used t o r e l a t e j o i s t s p l i c e n a i l i n g t o t h e h e e l j o i n t n a i l i n g . T h i s r u l e ( t h a t t h e j o i s t s p l i c e r e q u i r e s one n a i l more t h a n t h e h e e l j o i n t ) had been e s t a b l i s h e d from a l i m i t e d s e r i e s of t e s t s on one type and s i z e of frame. I n t h e p r e s e n t s e r i e s t h e r u l e was a p p l i e d t o frames of d i f f e r e n t s p a n s and s l o p e s w i t h s a t i s f a c t o r y r e s u l t s . Only f i v e of t h e 21 t e s t s had f a i l u r e a t t h e s p l i c e f i r s t .

The f a c t t h a t no f a i l u r e s o c c u r r e d i n t h e members i n d i c a t e s t h a t even w i t h t h e c a l c u l a t e d n a i l i n g t h e roof frames do n o t

-

provide a balanced d e s i g n . To a c h i e v e a balanced d e s i g n ( i . e . s t r e n g t h of n a i l i n g matching s t r e n g t h of members), e i t h e r t h e n a i l i n g would have t o be i n c r e a s e d o r t h e s t r e n g t h of

members would have t o be reduced. However, s i n c e t n e n a i l i n g i s based on c e r t a i n assumptions and provided t h e r e q u i r e d s t r e n g t h s i n t h e t e s t s , it would be i l l o g i c a l t o b a l a n c e t h e d e s i g n by f u r t h e r i n c r e a s e i n t h e n a i l i n g . The a l t e r n a t i v e of r e d u c i n g t h e s t r e n g t h of t h e members would seem t o be p r e f e r a b l e , provided c o n s i d e r a t i o n s o t h e r t h a n s t r e n g t h a r e n o t o v e r - r i d i n g .

APPLICATION OF RESULTS

For p r a c t i c a l a p p l i c a t i o n of t h e c a l c u l a t e d n a i l i n g , two ~ o i n t s should be c o n s i d e r e d which do n o t e n t e r i n t o t h e c a l c h a t i o n s

.

These concern t h e minimum and maximum number of n a i l s which should and can be u s e d , r e s p e c t i v e l y , a t t h e h e e l j o i n t .

Regarding t h e minimum number of n a i l s it i s p o s s i b l e t h a t , i n some c a s e s , l o a d s o t h e r t h a n t h e dead and snow l o a d s w i l l r e q u i r e more n a i l s t h a n h a s been c a l c u l a t e d . If t h e t o t a l wind s u c t i o n f o r c e exceeds t h e weight of t h e r o o f , t h i s w i l l r e v e r s e t h e f o r c e s a t t h e h e e l j o i n t s and s t r e s s t h e t o e n a i l s i n withdrawal. The anchorage of t h e r o o f a g a i n s t l i f t i n g by wind i s , however, o u t s i d e t h e scope of t h i s r e p o r t .

The maximum number of n a i l s a t t h e h e e l j o i n t i s l i m i t e d i n p r a c t i c e by t h e a v a i l a b l e n a i l i n g space i n t h e members. The problem does n o t a r i s e a t t h e j o i s t s p l i c e

s i n c e it can be l e n g t h e n e d t o accommodate any number of n a i l s .

A t t h e h e e l j o i n t , however, t h e a v a i l a b l e a r e a i s governed by t h e roof s l o p e and by t h e s i z e s of t h e r a f t e r s and j o i s t s , h i g h s l o p e s and s m a l l menbers g i v i n g t h e l e a s t a r e a . Member s i z e s depend, i n t u r n , on t h e span and on t h e s p e c i e s and

grade of lumber used. Again, however, a s f o r minimum n a i l i n g ,

it i s n o t t h e i n t e n t of t h i s r e p o r t t o c o n s i d e r t h e q u e s t i o n i n d e t a i l b u t merely t o p o i n t o u t t h e problem and i t s f a c t o r s .

COBCLUS I ON

Agreement h a s been found between t h e c a l c u l a t e d and t h e e x p e r i m e n t a l f a i l u r e l o a d s , g i v i n g c o n f i d e n c e i n t h e

procedure used i n c a l c u l a t i n g t h e number of n a i l s r e q u i r e d t o provide a l o a d f a c t o r ( r a t i o of f a i l u r e l o a d t o d e s i g n l o a d ) of 2 a g a i n s t f a i l u r e . I t can be concluded t h a t t h e n a i l i n g shown i n Tables I , I1 and I11 could s e r v e a s a b a s i s f o r t h e f o r m u l a t i o n of a new n a i l i n g s c h e d u l e . Although such a n a i l i n g s c h e d u l e would r e p r e s e n t a c o n s i d e r a b l e advancement, t h e r e may be o t h e r f a c t o r s , such a s p r a c t i c a l c o n s i d e r a t i o n s , which might determine t o what e x t e n t r e f i n e m e n t s c a n be p u t

i n t o p r a c t i c e .

Even more i m p o r t a n t , however, i s t h e q u e s t i o n of what s t r e n g t h o r margin of s a f e t y i s d e s i r a b l e i n r e s i d e n t i a l roof f r a m i n g and how a "bal.anced d e s i g n " ( e q u a l s t r e n g t h i n members and n a i l i n g ) can be a c h l e v e d .

The n a i l i n g s u g g e s t e d i n t h i s r e p o r t i s aimed a t a l o a d f a c t o r of 2 f o r t h e n a i l e d c o n n e c t i o n s , a s i s r e q u i r e d a t p r e s e n t by C e n t r a l Mortgage and Housing C o r p o r a t i o n and t h e 1363 Housing S t a n d a r d s f o r t r u s s e s . To a c h i e v e t h i s l o a d

f a c t o r i n terms of c u r r e n t d e s i g n snow l o a d s , c o n s i d e r a b l y s t r o n g e r n a i l i n g would be r e q u i r e d i n c o n v e n t i o n a l frames t h a n h a s been common p r a c t i c e i n t h e p a s t , b u t t h e s i z e of t h e members could be reduced.

There may be some who would a r g u e t h a t a n y i n c r e a s e i n s t r e n g t h over t h a t p r e s e n t l y o b t a i n e d i s unwarranted i n view of t h e a p p a r e n t l y s a t i s f a c t o r y performance of p r e s e n t r o o f s . Yet, a l t h o u g h it i s t r u e t h a t t h e g r e a t m a j o r i t y of r o o f s i n Canada a r e s t a n d i n g up s u c c e s s f u l l y ( i n c l u d i n g t h o s e b u i l t a t a time when t h e d e s i g n snow l o a d w a s assumed t o be 4 0 psf a l m o s t everywhere, w i t h o u t c o n s i d e r a t i o n of v a r i a t i o n s of s n o w f a l l ) , it i s a l s o t r u e t h a t t h e r e have been some f a i l u r e s i n r o o f s due t o snow l o a d s . U n f o r t u n a t e l y , t i s p r a c t i c a l l y i m p o s s i b l e t o f i n d o u t how many f a i l u r e s o c c u r r e d i n c o n v e n t i o n a l r o o f s n o r t o what e x t e n t f a u l t y workmanship and d e f e c t s have been c o n t r i b u t i n g f a c t o r s .

C o n s i d e r i n g t h e low s t r e n g t h found by t e s t s i n some t y p e s of c o n v e n t i o n a l r o o f frames commonly b u i l t i n t h e p a s t , it i s indeed s u r p r i s i n g t h a t t h e r e have been s o few r e p o r t s of f a i l u r e s . T h i s may s u g g e s t t h a t t h e d e s i g n snow l o a d s a r e perhaps t o o h i g h f o r a v e r a g e c o n d i t i o n s (exposure t o wind e t c . )

.

Since it i s d i f f i c u l t t o base t h e choice of t h e

r e q u i r e d s t r e n g t h on r e c o r d s of s a t i s f a c t o r y o r u n s a t i s f a c t o r y performance, r e c o r d s which do n o t e x i s t , it would seem more a p p r o p r i a t e , a s suggested by t h e approach followed i n t h i s r e p o r t , t o base minimum requirements f o r t h e s t r e n g t h of r o o f s on an engineering approach, g i v i n g due c o n s i d e r a t i o n t o f a c t o r s of s a f e t y used i n o t h e r c l a s s e s of s t r u c t u r e s .

It seems a f a c t t h a t a lower f a c t o r of s a f e t y can be accepted i n houses t h a n can be accepted i n l a r g e r t i m b e r s t r u c t u r e s i n which t h e allowable s t r e s s e s used provide a n average

f a c t o r of s a f e t y of t h e o r d e r of

3

t o 5. Obviously, however, one does n o t want t o go t o o f a r i n lowering t h e s a f e t y margin i n houses. I n any case it i s e v i d e n t t h a t margins of s a f e t y can only be more c l e a r l y e s t a b l i s h e d and c o n t r o l l e d t o t h e e x t e n t t h a t snow l o a d s on r o o f s t o be expected i n t h e v a r i o u s r e g i o n s a c r o s s Canada become more a c c u r a t e l y h o r n . Work on t h i s l a t t e r a s p e c t i s c u r r e n t l y being c a r r i e d out by t h e Division of Building Research.

REFERENCE

1. Thorburn, H. J. and B. G. W. P e t e r . Loading t e s t on j o i s t and r a f t e r roof frames. National Research Council, Division of Building Research, I n t e r n a l Report No. 225, Ottawa, J u l y 1961.

TABLE I

CALCULATED NUiPBER OF TH2OUGH HAILS REQUIIIED AT HEEL JOINTS

TO IBSIST A DESIGN LIVE LOAD OF 30 PSF

S l o p e 4 i n 1 2

5

i n 1 2 6 i n 1 2

7

i n 1 2 9 i n 1 2 1 2 i n 1 2 Frame s p a c i n g ( i n . ) 1 2 1 6 24 1 2 1 6 24 1 2 1 6 24 1 2 1 6 24 1 2 1 6 24 1 2 1 6 24 .. 1 6 a n d l e s s 2 3

5

1 2 4 1 2

7

0 0 2 0 0 1 0 0 0 Span 1 6 . 1 - 2 0 3 4 6 2 3

5

1 2 4 1 1 2 0 1 2 0 0 1 ( f t ) 20.1-24 3

5

8 3 4 6 2 3

5

1 2

3

1 1 2 0 0 1 24.1-28 4 6 9 3 4 7 2 4 6 1 2 4 1 1 3 0 0 1 28.1-32

5

7

11 4

5

8 3 4

7

2

3

4 1 2 3 0 1 1

TABLE I1

CALCULATED NUMBER OF THROUGH NAILS Rl3QUIFG2D AT HEEL JOINTS TO RESIST A DESIGN LIVE LOAD OF 40 PSB

S l o p e 4

i n

1 2

5

i n

1 2 6

i n

1 2

7

i n

1 2 9

i n

1 2 1 2 i n 1 2 - Frame s p a c i n g ( i n . ) 1 2 1 6 : 24 1 2 16' 24 1 2 1 6 24 1 2 1 6 24 1 2 1 6 24 1 2 1 6 24 I 1 6 a n d l e s s 3 4 7 2

3

5

2 2 4 1 1

3

0 1 2 0 0 1 1 6 . 1 - 2 0 4

5

9

3

4 7 2 3

5

1 2

3

1 1 2 0 0 1 Span ( f t ) 20.1-24

5

7

11 4

5

8

3

4

7

2

3

4 1 2

3

0 1 1 24.1-28 6 8

1 3

4 6 1 0 3

5

8 2

3

5

1 2 4 0 1 2 28.1-32

7

9 1 5

5

7

11 4

6

9

3

4 6 2

3

5

1 1 2

-

TABLE 111

CALCULATED NUiBER OF THROUGH NAILS mQUIRED AT HEEL JOINTS TO ZESIST A DESIGN LIVE LOAD OF 5 0 PSF

S l o p e 4 in 1 2 5 in 1 2

6

in 1 2

7

in 1 2

9

in 1 2 1 2 in 1 2

Frame

spacing (in. ) 1 2 1 6 24 1 2 1 6 24 1 2 1 6 24 1 2 1 6 24 1 2 1 6 24 1 2 1 6 24 1 6 and l e s s

4

5

9

3

4

7

2

3

5

1 2

3

1 1 2 0 0 1 Span 1 6 . 1 - 2 0 5

7

11 4

5

9

3

4

7

2

3

5 1 2

3

0 1 1 (ft) 2 0 - 1 - 2 4 6

9

13

5

7

10 4 5

9

2

3

6

2 2 4 0 1 2 2 4 - 1 - 2 8

7

10 1 6 6 8 1 2 5 6 1 0

3

4

7

2

3

5 1 1 2 2 8 - 1 - 3 2 8 1 2 18

7

9

1 4

5

7

1 2

3

5

8 2 4 6 1 2

3

TABLE I V

.SUifZi;ARY OF LOADIWG TEST RESULTS

% Average v a l u e s f r o m p r e v i o u s t e s t s . ( ) Values i n b r a c k e t s i n d i c a t e s e c o n d a r y j o i n t f a i l u r e . Second t e s t p e r f o r m e d a f t e r r e p a i r . Span f t 24 24 24 2 4 28 28 28 2 8

Note: ie. " ~ a l c u l a t e d " and " F a i l u r e Load" u n i t s . The l o a d i s g i v e n i n l b / f t ( r a t h e r t h a n l b / f t 2 )

-

_{b e c a u s e o f t h e v a r i o u s r a f t e r s p a c i n g s c o n s i d e r e d . The l o a d s a r e somewhat l o w e r f o r} t h e 9/12 s l o p e b e c a u s e a s l o p e r e d u c t i o n f o r snow l o a d s of 0 . 8 a p p l i e s t o s l o p e s of 3 0 t o 40 deg. No. o f N a i l s a t Heel 5 8 1 3 4 7 1 0 3 5 8 1 2 4 6 1 0 1 6 4 8 1 2 3 6 1 0 1 3 5 Frame S l o p e /12 4 4 4 5 5 5 6 6 6 9 9 9 4 4 4 5 5 5 6 6 6 9 9 9 S p a c i n g i n . 1 2 1 6 2 4 1 2 1 6 24 1 2 1 6 24 1 2 1 6 24 1 2 1 6 24 1 2 1 6 2 4 1 2 1 6 24 1 2 1 6 24 I a f t e r S i z e 2 x 4 2 x 6 2 x 6 2 x 4 2 x 4 2 x 4 2 x ₄ 2 x 6 2 x 6 2 x 4 2 x 6 2 x 6 2 x 6 2 x 6 2 x 6 2 x 6 2 x 6 2 x 6 2 x 6 2 x 6 2 x ₆ 2 x 6 2 x 6 2 x 6 C a l c u l a t e d Load ( l b / f t ) ao+6 133+8 200+12 80+6 l 3 3 + 8 200+12 eo+6 133+8 200+12 64+6 l 0 7 + e 160+12 80+6 133+8 200+12 80+6 133+8 200+12 80+6 133+8 200+12 64+6 107+8 160+12 P e r C e n t o f C a l c u l a t e d Load 106 9 2 1 0 8 1 1 0 1 0 5 9 4 116 8 5 ( 7 5 ) 8 0 1 1 2 8 6 87 9 3 78 9 0 1 0 5 96 ( 7 7 ) 92 1 0 4 1 1 9 (78 ) 8 2 ( 1 0 0 ) 106 ( 9 0 )88 (88 1105 L e f t h e e l 9 1 1 3 0 230 95* 1 4 8 3 2000 100 1 2 0 9 0 9 9 1 4 9 8 0 1 9 0 90 1 9 5 1 7 3 74 1 8 0 F a i l u r e L e f t c o l l a r ( 1 0 4 ( 1 5 2 ) Load ( J o i s t s p l i c e ( 1 6 0 ) 90 (164 ( 1 6 6 ) ( 7 0 ) l b / f t ) R i g h t c o l l a r 90 R i g h t h e e l 1 7 0 1 1 0 1 3 5 1 0 2 147 1 0 1