A Beginner's Guide to the Steel Construction Manual, 13^th ed. (old)

Chapter 5 - Welded Connections

© 2006, 2007, 2008, 2009 T. Bartlett Quimby

Section 5.9

Homework Problems

As presented in Chapter 1, the homework problems involve the design of elements of three different structures plus some unrelated details.  Please see the relevant links below for each structure.  When completing the problems, consider both ASD and LRFD design philosophies unless otherwise specified by the instructor.  Consider all limit states presented in this and prior chapters.  Consider developing a generic spreadsheet that you can apply to similar problems.

Miscellaneous Steel Problems

Problems M5.1:   MISCDET_STL_STL 1/S2.2 shows a braced pile system for a dock structure located in Whittier, Alaska.   The drawing is not an accurate as-built drawing.  Assume an E70XX electrode has been used.  Express your results in terms of service load levels assuming that the applied load is 0.5 part dead load, 0.5 parts live load, and 1.75 part seismic load.

• Problem M5.1a:  Determine the capacity of the weld that connects the diagonal brace to the gusset plate as shown in the detail.  Consider both the strength of the weld and the base metal.  Ignore any eccentricity.
• Problem M5.1.b:  Is this a "balanced" weld?  If not, what is the eccentricity and how will it affect the capacity of the connection?

Problem M5.2:  MISCDET_STL 2/S2.1 shows two MC sections attached to a gusset plate.  Using a 1/2" thick gusset plate, a pair of C10x30 channels, E70XX electrodes and A588 steel design a fillet welded connection that is 50% stronger than the channels in tensile yielding.  Neatly draw a scaled detail of the connection.  Note:  There are a number of situations where parts of a structure are designed to be stronger than other parts, regardless of structural analysis results.  This is typically done to ensure that a particular failure mode will not control the design.  In this case, failure would be tensile yielding of the brace instead of fracture of the connection!

Problem M5.3:  For this problem refer to drawing MISCDET_STL 4/S2.1.  A pair of L3x3x5/16 are welded to a 7/16" thick gusset plate with fillet welds as shown.  Use E70XX electrodes.  Design the connection to have a balanced weld group and to have a capacity 25% greater than the tensile yielding capacity of the angles.

Problems M5.4:  For this problem refer to drawing MISCDET_STL 4/S5.1.  Create a general purpose spreadsheet (in MS Excel unless otherwise approved by your instructor) to compute the capacity, P_n for the fillet welded connection shown.  Consider only weld strength.  The design variables are the weld leg size "a", electrode type and grade, the distances A and B, the location of the force (X), and the angle of loading (Angle) from the vertical.  Group the design variables and the resulting value at the beginning of the spreadsheet.

Problem M5.4a:  Use the Elastic Vector method
Problem M5.4b:  Use the Instantaneous Center of Rotation method.

Problems M5.5:  For this problem refer to drawing MISCDET_STL 5/S5.1.  Create a general purpose spreadsheet (in MS Excel unless otherwise approved by your instructor) to compute the capacity, P_n for the fillet welded connection shown.  Consider only weld strength.  The design variables are the weld leg size "a", electrode type and grade, the distances A and B, and the location of the force (X).  Group the design variables and the resulting value at the beginning of the spreadsheet.

Problem M5.6:  Using the connection in MISCDET_STL 1/S1.3, assume that the W section is a W14x30 and the plates are all 3/8" thick.  F7XX electrodes are used.  Determine the minimum practical length "L" for which the weld connection is at least as strong as the bolted connection.  Note that all welds are equally stressed since they deform equally.

Problem M5.7:  Using the connection in MISCDET_STL 1/S1.3, assume that the W section is a W16x31, the plates are all 1/2" thick, and L = 16".  Determine the maximum moment nominal moment, M_n, that the welded connection can transfer.  Consider that only the flange plates are effective in transferring moment.  Recall that moment equals the couple formed by the weld forces on each flange times the distance between the center of the connection plates.

Dormitory Building Design Problems

The braces in this building may be connected to the frames by welds, depending on the detail used.  In these problems, the connections will be designed based on weld strength and shear rupture of the base metal.

Problem D5.1:  For a brace on the first floor level on Grid 2 and between Grids A & B determine the required size and length of fillet weld to carry the required force while minimizing the lap length, L, between the brace and gusset plate.  Assume that the gusset plate is 7/16" thick.  Neatly draw a scaled detail of the final connection.

• Problem D5.1a:  Assume that the brace consists of a pair of angles (L4x4x3/8) and is connected to the frame by a connection similar to MISCDET_STL 4/S2.1. 
• Problem D5.1b:  Assume that the brace is an HSS 5x5x1/4 and is connected to the frame by a connection similar to MISCDET_STL 5/S2.1.

Problem D5.2:  Repeat Problem D5.1 for the other braces in the structure.  Complete the following table by entering the weld leg size and the minimum required lap length, L, in each cell:

On Grid	Between Grids	Level	Problem #
			D5.2a		D5.2b
			ASD	LRFD	ASD	LRFD
2	A & B	3
		2
		1
	P & R	3
		2
		1
11	A & B	3
		2
		1
	P & R	3
		2
		1

Problem D5.3:  A beam to column connection similar to that shown in MISCDET_STL 3/S3.1 (A = 3", B = 8", and the plate is 3/8" thick) is to be used to connect the second floor beams on grid C between grids 3 & 9 (see the floor framing plan on DORM S1) to the columns at either end of the beams. The beams support 3'-4" of the corridor on one side and 6'-3" of dorm room on the other along their lengths.  They also support a 10 ft tall interior wall along their lengths.  Compute the reactions for the beams then determine the minimum required weld size to connect the plate to the column flange.  Consider a load arrangement where one beam supports live load while the other does not so as to cause the greatest unbalanced load on the connecting plate.

Problem D5.4: A beam to column connection similar to that shown in MISCDET_STL 4/S3.1 (A = 4", B = ", and the plate is 3/8" thick) is to be used to connect the second floor beam on grid 6 between grids E & G (see the floor framing plan on DORM S1) to the column a the intersection of grids 6 & E. The beam supports 7'-7" of the dorm room and 10'-8" exterior wall along its length.  Compute the reactions for the beam then determine the minimum required weld size to connect the plate to the column flange.  Assume the center of the beam reaction is at the center of the bearing plate.

Tower Design Problems

The tower diagonal braces are connected to the tower legs via gusset plates welded to the tower legs.  In the alternate connection details, end plates are welded to the brace members so that the braces can be bolted to the legs. 

Problem T5.1:  Select the appropriate electrode for the SAW process and determine the size and length of fillet weld required to connect a gusset plate to the tower leg in order to transfer twice a level D brace force as shown in TOWER 3/S2.  Note that the detail shows a level C and Level D brace connecting to the tower leg.

Problem T5.2:  Select the appropriate electrode for the SMAW process and determine the size of fillet weld needed to connect tower leg segment 2 to its connection plate where it is bolted to tower leg segment 1 as shown in TOWER 2/S2.  Assume that the tower leg is an 8" dia. standard steel pipe section and that the connection plate is 3/4" thick.

Problem T5.3:  Select the appropriate electrode for the SMAW process, determine the minimum required lap length, L, and the associated fillet weld leg size, a, for the connection shown in TOWER 2/S3.  Assume that the brace is a round HSS3.000x.216 and the end plate is 1/4" thick.

Truss Bridge Design Problems

The bridge has all bolted connections, however, for this chapter, we will investigate the use of partially welded connections. 

Problem B5.1:  Detail TBRDG 2/S4 shows an alternative to the actual connection detail shown in TBRDG 5/S4, the difference being the connection angles being welded to the web of the girder.  Assuming that the girder is a W27x84 and the connection angles are a pair of L6x3.1/2x1/2 (long legs back-to-back), what maximum reaction can the girder have based on the weld strength?  Assume F7XXX electrodes.

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