REVIEW LECTURE #1KNOWLEDGE BASE REQUIRED:

STRENGTH OF MATERIALSSTEEL DESIGNTIMBER DESIGNSOIL MECHANICS

WE COVERED:AREA AND CENTER OF GRAVITYItotxx = Ixx + Ay2

RADIUS OF GYRATION SECTION MODULUS

SOLVED ONE PROBLEM

MECHANICS OF MATERIAL BEHAVIOR:

DEFLECTION COMPUTATIONS

SOLVED DEFLECTION PROBLEM• DUE TO LOAD• DUE TO THERMAL EXPANSION

WE REVIEWED STATICS:

WE REVIEWED FLEXURE:

SM

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REVIEW OF STATICS (CONT’D)

MOMENT -SHEAR DIAGRAMS

SAMPLE PROBLEM

2' 6 ' 4 '

16000# 14000#

12000# 18000#

4000LB

-14000LB

32000FT-LB

56000 FT-LB

SOLUTION

SIMPLE SUPPORT

CANTILEVER

OVERHANGING

CONTINUOUS

IN FORMING AND BRACING DESIGN MANY OF THE MEMBERS HAVE MULTIPLE SUPPORTS.

WHAT IS THE DIFFERENCE BETWEEN A CONTINOUS MEMBER AND A SIMPLE SPAN??

Will the Moments be higher for the simple span or the continuous span??

Will the Shear be higher for the simple span or the continuous span??

Will the loads be higher for the simple span or the continuous span??

IN FORMING AND BRACING DESIGN MANY OF THE MEMBERS HAVE MULTIPLE SUPPORTS.

A B C D

w l

ASSUME A SPAN OF 10 FT. AT 1K/FT:

A=5k B=10k C D

w =1k/ft

.5w l

Vm ax=.5w l=5K

.5w l .5w l

M m ax=12.5 K -FT

SIMPLE SPAN SOLUTION

CONTINUOUS BEAMS - THREE SPANS

A=4k B=11k C D

w =1k/ft

.4w l

Vm ax=.6w l=6K

.5w l

.4w l.4w l

.6w l

M m ax=10K-FT

CONTINUOUS SPAN SOLUTION

CONCLUSION:

NOTE:• A Continuous Span will have: 10% more load on its interior

supports than a simple span20% less load on the exterior

support than a simple span

• Shear is greater in the continuous span solution 6K > 5K

• The maximum moment is greater in the simple span solution 12.5 k-ft > 10 k-ft

CONCLUSION CONTINUED:

• The length of the Wood member would have to span over all of the supports of the beam as one piece, because it is difficult to splice different member together effectively to achieve continuity!!

• Steel members would have to be the length of the full member because you can splice the pieces together, but welds and bolts are not sufficient enough to prevent stress concentrations across the connections!!