Method and apparatus for in situ assemblage of a strain sensor in erected structural elements

• US 4,738,135 A
• Filed: 12/15/1986
• Issued: 04/19/1988
• Est. Priority Date: 12/15/1986
• Status: Expired due to Term

• Current Assignee: Thermedics, Inc. (Thermo Fisher Scientific Incorporated)
• Original Assignee: Ramsey Engineering Company
• Inventors: Cadwell, Lawrence O., Schneider, Paul T., Boyle, Bradley C.
• Primary Examiner(s): Levy, Stewart J.
• Assistant Examiner(s): Raevis, Robert R.
• Application Number:
  US06/941,720
• Time in Patent Office: 491 Days
• Field of Search: 73/786, 73/768, 29/595, 408/72 R
• US Class Current: 73/786
• CPC Class Codes: G01G 13/16 Means for automatically discharging weigh receptacles under control of the weighing mechanism
• CPC Class Codes: G01G 19/52 Weighing apparatus combined with other objects, e.g. furniture with walking sticks A45B3/08
• CPC Class Codes: G01G 21/23 Support or suspension of weighing platforms G01G21/24 takes precedence
• CPC Class Codes: G01G 3/1402 Special supports with preselected places to mount the resistance strain gauges; Mounting of supports
• CPC Class Codes: G01L 1/2287 constructional details of the strain gauges adjustable resistors H01C10/00

Abstract

A method and apparatus for in situ drilling of a precise hole in an erected structural element and inserting in such hole in pressed-fit relationship a cylindrical strain gauge. A guide block is provided having a precision hole corresponding to the diameter of the hole desired in the structural element. The guide block has unthreaded bolt holes for attachment of the guide block to the structural element and guides a reamer to produce a precise hole in the structural element. The guide block also has threaded holes for advancing a push plate against a force-transmitting bushing which is insertable through the precision hole in the guide block into abutting relationship with an end face of a cylindrical strain gauge to force the gage into press-fit relationship with the precise hole in the erected structural element.

Claims

1. A method of in situ press-fit assembly of a cylindrical strain sensor in a portion of a structural steel element, said cylindrical strain sensor having a central maximum diameter portion and at least one reduced-diameter end portion, comprising the steps of:

(1) providing a guide block having a central hole with a diameter less than the maximum diameter of the cylindrical strain sensor by an amount equal to the desired press-fit interference, and a counterbore sized to freely receive an end portion of said cylindrical strain sensor therein, a pair of unthreaded bolt holes radially spaced from said central hole, and a plurality of threaded holes disposed in peripherally spaced relation to said central hole;

(2) fabricating a template having center punch indications respectively alignable with the axes of said center hole and said unthreaded said bolt holes;

(3) abutting said template with the portion of the structural steel element where stress determination is desired;

(4) center punching hole locations in said portion through said center punch indications in said template;

(5) drilling a pilot hole at said center punch location corresponding to said central hole to a diameter less than the maximum diameter of said cylindrical strain sensor;

(6) drilling holes at each center punch location of said unthreaded bolt holes to a diameter equal to said unthreaded bolt holes;

(7) securing said guide block to the surface of said portion by bolts snugly traversing said unthreaded holes in said guide block and the aligned holes in said portion of the structural steel element, and securing said bolts with nuts applied to the ends of said bolts projecting through the structural steel element;

(8) inserting a counterbore reamer through said center hole of said guide block and finishing said pilot hole in said portion of the structural steel element to a diameter less than the maximum diameter of said cylindrical strain sensor by an amount equal to the desired press-fit interference;

(9) removing said guide block from said portion of the structural steel element;

(10) inserting a reduced-diameter end portion of said cylindrical sensor in said finished hole in said portion;

(11) reassembling said guide block to said portion with said maximum diameter portion of said cylindrical sensor disposed in said counterbore;

(12) inserting a force-transmitting bushing in said central hole in said guide block with one end of said bushing projecting out of said central hole;

(13) securing a push plate across the projecting end of the said force-transmitting bushing by bolts traversing the push plate and threaded into said threaded holes of said guide block; and

3. The method of claim 1 wherein said cylindrical strain sensor has electrical leads projecting axially therefrom and further comprising the step of passing said electrical leads axially through said central hole and said force-transmitting bushing prior to the press-fitting of said cylindrical strain sensor into said finished hole.

5. The apparatus of claim 3 further comprising a counterbore in one end of said central guide hole for receiving an end portion of said cylindrical strain gauge element therein preliminary to the forcing of said cylindrical strain gauge into said precise diameter hole.

7. The method of claim 5 wherein said cylindrical strain sensor has electrical leads projecting axially therefrom and further comprising the step of passing said electrical leads axially through said central hole and said force-transmitting bushing prior to the press-fitting of said cylindrical strain sensor into said finished hole.

2. (14) sequentially tightening said last-mentioned bolts to force said cylindrical strain sensor into said finished hole in the structural steel element in press-fit relationship thereto.

4. Apparatus for producing, in situ, a precise diameter hole in a portion of an installed structural steel element and press-fitting a cylindrical strain gauge sensor in the precise diameter hole, comprising a metallic guide block having a face abuttable with said portion;

a central guide hole traversing said guide block in perpendicular relation to said face;

said guide hole having a bore diameter substantially equal to but not less than the desired diameter of the hole to be drilled in said portion;

a first pair of non-threaded bolt-receiving holes traversing said guide block in perpendicular relation to said face and spaced on opposite sides of said guide hole;

a template for center punching said portion at locations corresponding to the axes of said central guide hole and said bolt-receiving holes, whereby a pilot hole and two bolt-receiving holes may be produced in said portion;

first bolt means for securing said guide block to said portion by traversing said unthreaded bolt-receiving holes;

a counterbore reamer snugly insertable through said central hole to finish said precise diameter hole in said portion;

a second pair of threaded holes traversing said guide block in perpendicular relation to said face and peripherally spaced intermediate said first pair of non-threaded holes;

a force-transmitting bushing slidably insertable in said guide hole;

a pressure plate having two unthreaded holes respectively alignable with said second pair of threaded holes;

second bolt means traversing said unthreaded holes in said pressure plate and engaging said second pair of threaded holes;

said pressure plate being abuttable with one end face of said force-transmitting bushing, whereby said cylindrical strain sensor may be forced by said bushing into said precise diameter hole in press-fitting relationship therewith by tightening said second bolt means.

6. A method of in situ press-fit assembly of a cylindrical strain sensor in a portion of a structural steel element, said cylindrical strain sensor having a central maximum diameter portion and at least one reduced-diameter end portion, comprising the steps of:

(1) providing a guide block having a central hole with a diameter less than the maximum diameter of the cylindrical strain sensor by an amount equal to the desired press-fit interference, and a counterbore sized to freely receive an end portion of said cylindrical strain sensor therein, a pair of unthreaded bolt holes radially spaced from said central hole, and a plurality of threaded holes disposed in peripherally spaced relation to said central hole;

(2) drilling a pilot hole in said portion and two bolt receiving holes in axial alignment with said central hole and said unthreaded bolt holes in said guide block;

(3) securing said guide block to the surface of said portion by bolts snugly traversing said unthreaded holes in said guide block and the aligned holes in said portion of the structural steel element, and securing said bolts with nuts applied to the ends of said bolts projecting through the structural steel element;

(4) inserting a counterbore reamer through said central hole of said guide block and finishing said pilot hole in said portion of the structural steel element to a diameter less than the maximum diameter of said cylindrical strain sensor by an amount equal to the desired press-fit interference;

(5) removing said guide block from said portion of the structural steel element;

(6) inserting a reduced-diameter end portion of said cylindrical sensor in said finished hole in said portion;

(7) reassembling said guide block to said portion with said maximum diameter portion of said cylindrical sensor disposed in said counterbore;

(8) inserting a force-transmitting bushing in said central hole in said guide block with one end of said bushing projecting out of said central hole;

(9) securing a push plate across the projecting end of the said force-transmitting bushing by bolts traversing the push plate and threaded into said threaded holes of said guide block; and

(10) sequentially tightening said last-mentioned bolts to force said cylindrical strain sensor into said finished hole in the structural steel element in press-fit relationship thereto.

8. Apparatus for producing, in situ, a precise diameter hole in a portion of an installed structural steel element having a curved exterior surface and press-fitting a cylindrical strain gauge sensor in the precise diameter hole, comprising a metallic guide block having a recessed face permitting non-rockable engagement of the guide block with said curved surface;

a central guide hole traversing said guide block in perpendicular relation to said face;

said guide hole having a bore diameter substantially equal to but not less than the desired diameter of the hole to be drilled in said portion;

a first pair of non-threaded bolt-receiving holes traversing said guide block in perpendicular relation to said face and spaced on opposite sides of said guide hole;

a template for center punching said portion at locations corresponding to the axes of said central guide hole and said bolt-receiving holes, whereby a pilot hole and two bolt receiving holes may be produced in said portion;

first bolt means for securing said guide block to said portion by traversing said unthreaded bolt-receiving holes;

a counterbore reamer snugly insertable through said central hole to finish said precise diameter hole in said poriton;

a second pair of threaded holes traversing said guide block in perpendicular relation to said face and peripherally spaced intermediate said first pair of non-threaded holes;

a force-transmitting bushing slidably insertable in said guide hole;

a pressure plate having two unthreaded holes respectively alignable with said second pair of threaded holes;

second bolt means traversing said unthreaded holes in said pressure plate and engaging said second pair of threaded holes;

said pressure plate being abuttable with one end face of said force-transmitting bushing, whereby said cylindrical strain sensor may be forced by said bushing into said precise diameter hole in press-fitting relationship therewith by tightening said second bolt means.