Week 7:Truss Design & Connections

Question 1

List 3 benefits of using Truss HSS

Answer 1

1 - Lighter in weight
2- easier to transport
3- requires less cranes for erection
4-torsionally stiff

Question 2

How many steps involved in HSS Truss Design?

Answer 2

12

Question 3

Step 1 in HSS Truss design?

Answer 3

Determine Truss layout (panel lengths, span, depth)

Question 4

What is the typical range of span-to-depth ratio for HSS trusses to avoid excessive deflections?

Answer 4

10-14

Question 5

Step 2 in HSS Truss design?

Answer 5

Determine loads at connections and on members

Question 6

Step 3 in HSS Truss design?

Answer 6

Determine axial force in all members

Question 7

Step 4 in HSS Truss design?

Answer 7

Determine chord member sizes

Question 8

Step 5 in HSS Truss design?

Answer 8

Determine web member sizes

Question 9

What 4 factors affect chord member sizing in HSS Trusses?

Answer 9

Axial load
Corrosion protection
Tube wall slenderness
K=0.9 for compression chord

Question 10

What 3 factors affect web member sizing in HSS Trusses?

Answer 10

1-Axial load
2-tweb < tchors
3- K=0.75

Question 11

Step 6 in HSS Truss design?

Answer 11

Standardise the web member sizes

Question 12

What must you remember to check in step 6 of HSS Truss design?

“Standardise web member sizes”

Answer 12

Always check for availability in your region/country before you decide on a section

Question 13

Step 7 in HSS Truss design?

Answer 13

Layout your connections

Question 14

What 2 things must you remember while carrying out step 7 of HSS Truss design?

Answer 14

1-start with gapped connections

2-check that member sizes are within validity range

Question 15

Step 8 in HSS Truss design?

Answer 15

Check connection efficiencies of most heavily loaded connection

Question 16

What should you do if connection efficiencies or resistances are inadequate?

Answer 16

1-Try overlapped connections if gapped used initially

2-Modify the members and recheck the connections

Question 17

Step 9 in HSS Truss design?

Answer 17

Try overlapped connection and/or modify members if connection efficiencies and/or resistances are inadequate

Question 18

Step 10 in HSS Truss design?

Answer 18

Check effect of primary moments on chord design

Question 19

What are the substeps of step 10 of HSS Truss design?

Answer 19

1-determine member bending moments

2-consider moment due to eccentricity for chord members if e is outside validly limits

Question 20

What are the 2 ways to analyse a HSS Truss?

Answer 20

1-(if manually) pin-jointed analysis

2-(if using software) continuous chords with pin-ended web analysis

Question 21

Step 11 in HSS Truss design?

Answer 21

Check truss deflections under specified loads

Question 22

Step 12 in HSS Truss design?

Answer 22

Specify fillet welds (and leave weld design to fabricator)

Question 23

State 1 golden rule for good Truss design

Answer 23

Continuous chord members

Question 24

State the formula for calculation of HSS truss deflection

Answer 24

Total deflection = member deflection + connection deflection

Question 25

Where are double chord HSS trusses usually needed?

Answer 25

For Heavy loads or long spans

Question 26

Describe a Vierendeel truss

Answer 26

Moment-resisting truss without diagonals

Question 27

List the 6 types of HSS truss-type welded connections

Answer 27

1-K
2-X
3-T
4-Y
5-N
6-KT

Question 28

What determines if a connection is a K-connection?

Answer 28

When the punching load (Nsintheta) in one branch member is equal to 20% of the load in the other branch member on the same side of the connection

Question 29

What determines if a connection is a T-connection?

Answer 29

When the branch member is perpendicular to the chord

Question 30

What determines if a connection is a Y-connection?

Answer 30

When punching load (N sin theta) is equilibrated by beam shear in the chord and branch member is not perpendicular to chord

Question 31

What determines if a connection is an X-connection?

Answer 31

When the punching load (N sin theta) is transmitted through the chord and equilibrated by branch member on the opposite side

Question 32

If your eccentricity is negative, what type of connection layout are you probably dealing with?

Answer 32

Overlapped connection

Question 33

If your eccentricity is positive, what type of connection layout are you probably dealing with?

Answer 33

Gapped connection

Question 34

How many failure modes exist for HSS Truss connections?

Answer 34

7

Question 35

How many of the potential failure modes of HSS Truss connections involve the chord?

Answer 35

5

Question 36

How many of the potential failure modes of HSS Truss connections involve the branch members?

Answer 36

2

Question 37

List the 7 potential failure modes of HSS Trusses

Answer 37

Mode A-Plastic failure of chord face
Mode B-Punching shear failure of chord face

Mode C-Tension failure of branch member
Mode D-Local buckling of branch member

Mode E-Overall shear failure of chord
Mode F-Local buckling of chord walls/Local yielding in tension
Mode G-Local buckling of chord connecting face

Question 38

Which failure mode governs with medium-to-high branch-to-chord ratios?

Answer 38

Punching shear failure of chord

Question 39

In what type of HSS connection can Failure of chord sidewall (local buckling of chord wall) occur?

Answer 39

RHS matched box connections

Question 40

What failure mode applies to transfers plates?

Answer 40

Mode C-Tension failure of branch member

Question 41

What is the dominant failure mode for HSS Truss overlapped K-connections?

Answer 41

Mode D-Local buckling of branch member

Question 42

List 3 tips for optimising welded HSS connection design

Answer 42

1-use stocky chords
2-use thinner branches
3-consider gapped connections

Question 43

According to best practice, what is the lowest recommended value of theta (branch angles)?

Answer 43

30 degrees

Question 44

Why are CHS branches welded to RHS chords sometimes?

Answer 44

To avoid the need/cost of profiling CHS members to CHS chords