Detensioning apparatus for releasing a chuck on a prestressed strand

A detensioning apparatus, for use during a process of fabricating prestressed concrete, during which process a region in which concrete is to be poured includes at least two opposing abutments, one or more prestressing strands are run between opposing abutments, tensioned and held in tension, by clamps that engage the strands and bear against the opposing abutments, while concrete is poured into the region and cured;

• wherein each clamp includes a chuck having one or more jaws, and a surrounding strand chuck barrel, configured so that tension in the strand, between opposing abutments, prompts the chuck to be pressed against the strand to frictionally engage the strand;
• the detensioning apparatus comprising:
• a collar member, operably configured to be placed onto a prestressing strand, that has been tensioned and to which a strand clamp has been affixed, the collar member having a central bore, a first portion of which is operably configured to insertingly receive a strand chuck barrel, and a second portion of which is provided with a smaller inner diameter than the first portion, defining a shoulder configured to bear against at least a portion of an end of a strand chuck barrel;
• a separation member housing, operably configured to be insertingly received in the second portion of the central bore of the collar member;
• at least one separation member supported on the separation member housing, and operably configured for separating a chuck from a prestressing strand, after the tension in the strand causing the chuck to be prompted against the strand is balanced;
• the collar member being operably configured to be slid onto a free end of a prestressing strand, to a position surrounding a strand chuck barrel that is holding a strand in tension, such that upon exertion of tension between a free end of the strand and a strand chuck barrel, the collar member bears against the strand chuck barrel and prevents its movement, so that additional tension in the strand will cause the chuck to be drawn toward the at least one separation member contained within the collar member;
• the chuck of the strand clamp being fabricated at least in part, from magnetically responsive material, the at least one separation member further comprising:
• at least one magnetic member mounted on the separation member housing, so as to exert magnetic force on the one or more jaws, when the additional tension is applied to the strand the one or more jaws move with the strand until they come into contact with the at least one separation member, the at least one separation member holding the one or more jaws, allowing the strand to slide through the one or more jaws, thereby detensioning the strand.

A detensioning apparatus, for use during a process of fabricating prestressed concrete, during which process a region in which concrete is to be poured includes at least two opposing abutments, one or more prestressing strands are run between opposing abutments, tensioned and held in tension, by clamps that engage the strands and bear against the opposing abutments, while concrete is poured into the region and cured;

• wherein each clamp includes a chuck having one or more jaws, and a surrounding strand chuck barrel, configured so that tension in the strand, between opposing abutments, prompts the chuck to be pressed against the strand to frictionally engage the strand;
• the detensioning apparatus comprising:
• a collar member, operably configured to be placed onto a prestressing strand, that has been tensioned and to which a strand clamp has been affixed, the collar member having a central bore, a first portion of which is operably configured to insertingly receive a strand chuck barrel, and a second portion of which is provided with a smaller inner diameter than the first portion, defining a shoulder configured to bear against at least a portion of an end of a strand chuck barrel;
• a separation member housing, operably configured to be insertingly received in the second portion of the central bore of the collar member;
• at least one separation member supported on the separation member housing, and operably configured for separating a chuck from a prestressing strand, after the tension in the strand causing the chuck to be prompted against the strand is balanced;
• the collar member being operably configured to be slid onto a free end of a prestressing strand, to a position surrounding a strand chuck barrel that is holding a strand in tension, such that upon exertion of tension between a free end of the strand and a strand chuck barrel, the collar member bears against the strand chuck barrel and prevents its movement, so that additional tension in the strand will cause the chuck to be drawn toward the at least one separation member contained within the collar member;
• the separation member housing further comprising a first cylindrical member, having a central bore, for receiving a prestressing strand;
• the first cylindrical member having a diameter less than the diameter of the second portion of the central bore of the collar member, to enable insertion of the first cylindrical member into the second portion of the central bore of the collar member;
• the first cylindrical member further having a first end operably configured to support the at least one separation member, at a position proximate an outer end of the first portion of the central bore of the housing member;
• the separation member housing further comprising a second cylindrical member, having a central bore operably configured to receive the first cylindrical member, the second cylindrical member having an outer diameter operably configured to enable, at least a first end portion of the second cylindrical member to be insertingly received, at least in part, in the second portion of the central bore of the collar member.

A method for detensioning a prestressing strand, for use during a process of fabricating prestressed concrete, during which process a region in which concrete is to be poured includes at least two opposing abutments, and one or more prestressing strands are run between opposing abutments, tensioned and held in tension, by clamps that engage the strands and bear against the opposing abutments, while concrete is poured into the region and cured;

• wherein each clamp includes a chuck having from one or more jaws and a surrounding strand chuck barrel, configured so that tension in the strand, between opposing abutments, prompts the one or more jaws of the chuck to be pressed against the strand to frictionally engage the strand, while preventing movement of the strand in a first direction relative to the strand clamp;
• positioning a detensioning apparatus onto a prestressing strand that has been tensioned and to which a strand clamp is affixed, the detensioning apparatus including
• a collar member, operably configured to be placed onto a prestressing strand, that has been tensioned and to which a strand clamp is affixed, the collar member having a central bore, a first portion of which is operably configured to surround and insertingly receive the strand chuck barrel of the strand clamp which is affixed to the prestressing strand, and a second portion of which is provided with a smaller inner diameter than the first portion, defining a shoulder configured to bear against at least a portion of an end of the strand chuck barrel of the strand clamp which is affixed to the prestressing strand;
• a separation member housing, operably configured to be insertingly received in the second portion of the central bore of the collar member;
• at least one separation member supported on the separation member housing, and operably configured for separating a chuck from a prestressing strand, after the tension in the strand causing the chuck to be prompted against the strand is balanced, to permit movement of the strand in the first direction and in a second direction relative to the one or more chuck jaws, said second direction being substantially opposite to the first direction;
• the collar member being operably configured to be slid onto a free end of a prestressing strand, to a position surrounding a strand chuck barrel that is holding a strand in tension, such that upon exertion of tension between a free end of the strand and a strand chuck barrel, the collar member bears against the strand chuck barrel and prevents its movement, so that additional tension in the strand will cause the chuck to be drawn toward the at least one separation member contained within the collar member;
• sliding the collar member onto a free end of a prestressing strand, to a position surrounding a strand chuck barrel, and affixing the detensioning apparatus against an abutment;
• pulling on a free end of the prestressing strand, until the tension in the strand that causes the chuck to be prompted against the prestressing strand has been balanced;
• applying additional tension in the strand, to cause the chuck to be drawn toward the at least one separation member contained within the collar member;
• whereupon the at least one separation member causes the chuck to become separated from the strand, to enable repositioning of the prestressing strand and/or the strand clamp.

A method for detensioning a prestressing strand, for use during a process of fabricating prestressed concrete, during which process a region in which concrete is to be poured includes at least two opposing abutments, one or more prestressing strands are run between opposing abutments, tensioned and held in tension, by clamps that engage the strands and bear against the opposing abutments, while concrete is poured into the region and cured;

• wherein each clamp includes a chuck having from one or more jaws and a surrounding strand chuck barrel, configured so that tension in the strand, between opposing abutments, prompts the chuck to be pressed against the strand to frictionally engage the strand;
• positioning a detensioning apparatus onto a prestressing strand, which strand has been tensioned and to which a strand clamp has been affixed, the detensioning apparatus including
• a collar member, operably configured to be placed onto a prestressing strand, that has been tensioned and to which a strand clamp has been affixed, the collar member having a central bore, a first portion of which is operably configured to insertingly receive a strand chuck barrel, and a second portion of which is provided with a smaller inner diameter than the first portion, defining a shoulder configured to bear against at least a portion of an end of a strand chuck barrel;
• a separation member housing, operably configured to be insertingly received in the second portion of the central bore of the collar member;
• at least one separation member supported on the separation member housing, and operably configured for separating a chuck from a prestressing strand, after the tension in the strand causing the chuck to be prompted against the strand is balanced;
• the collar member being operably configured to be slid onto a free end of a prestressing strand, to a position surrounding a strand chuck barrel that is holding a strand in tension, such that upon exertion of tension between a free end of the strand and a strand chuck barrel, the collar member bears against the strand chuck barrel and prevents its movement, so that additional tension in the strand will cause the chuck to be drawn toward the at least one separation member contained within the collar member;
• sliding the collar member onto a free end of a prestressing strand, to a position surrounding a strand chuck barrel, and affixing the detensioning apparatus against an abutment;
• pulling on a free end of the prestressing strand, until the tension in the strand that causes the chuck to be prompted against the prestressing strand has been balanced;
• applying additional tension in the strand, to cause the chuck to be drawn toward the at least one separation member contained within the collar member;
• whereupon the at least one separation member causes the chuck to become separated from the strand, to enable repositioning of the prestressing strand and/or the strand clamp;
• the chuck of the strand clamp being fabricated, at least in part, from magnetically responsive material, the method further comprising the step of fabricating the at least one separation member as at least one magnetic member mounted on the separation member housing, so as to exert magnetic force on the one or more jaws, when the additional tension is applied to the strand the one or more jaws move with the strand until they come into contact with the at least one separation member, the at least one separation member holding the one or more jaws, allowing the strand to slide through the one or more jaws, thereby detensioning the strand.

A method for detensioning a prestressing strand, for use during a process of fabricating prestressed concrete, during which process a region in which concrete is to be poured includes at least two opposing abutments, one or more prestressing strands are run between opposing abutments, tensioned and held in tension, by clamps that engage the strands and bear against the opposing abutments, while concrete is poured into the region and cured,

• wherein each clamp includes a chuck having from one or more jaws and a surrounding strand chuck barrel, configured so that tension in the strand, between opposing abutments, prompts the chuck to be pressed against the strand to frictionally engage the strand,
• positioning a detensioning apparatus onto a prestressing strand, which strand has been tensioned and to which a strand clamp has been affixed, the detensioning apparatus including
• a collar member, operably configured to be placed onto a prestressing strand, that has been tensioned and to which a strand clamp has been affixed, the collar member having a central bore, a first portion of which is operably configured to insertingly receive a strand chuck barrel, and a second portion of which is provided with a smaller inner diameter than the first portion, defining a shoulder configured to bear against at least a portion of an end of a strand chuck barrel,
• a separation member housing, operably configured to be insertingly received in the second portion of the central bore of the collar member,
• at least one separation member supported on the separation member housing, and operably configured for separating a chuck from a prestressing strand, after the tension in the strand causing the chuck to be prompted against the strand is balanced,
• the collar member being operably configured to be slid onto a free end of a prestressing strand, to a position surrounding a strand chuck barrel that is holding a strand in tension, such that upon exertion of tension between a free end of the strand and a strand chuck barrel, the collar member bears against the strand chuck barrel and prevents its movement, so that additional tension in the strand will cause the chuck to be drawn toward the at least one separation member contained within the collar member,
• sliding the collar member onto a free end of a prestressing strand, to a position surrounding a strand chuck barrel, and affixing the detensioning apparatus against an abutment;
• pulling on a free end of the prestressing strand, until the tension in the strand that causes the chuck to be prompted against the prestressing strand has been balanced,
• applying additional tension in the strand, to cause the chuck to be drawn toward the at least one separation member contained within the collar member,
• whereupon the at least one separation member causes the chuck to become separated from the strand, to enable repositioning of the prestressing strand and/or the strand clamp
• the method further comprising the step of fabricating the separation member housing as a first cylindrical member, having a central bore, for receiving a prestressing strand,
• the first cylindrical member having a diameter less than the diameter of the second portion of the central bore of the collar member, to enable insertion of the first cylindrical member into the second portion of the central bore of the collar member,
• the first cylindrical member further having a first end operably configured to support the at least one separation member, at a position proximate an outer end of the first portion of the central bore of the housing member,
• the method further comprising the step of providing the separation member housing with a second cylindrical member, having a central bore operably configured to receive the first cylindrical member, the second cylindrical member having an outer diameter operably configured to enable, at least a first end portion of the second cylindrical member to be insertingly received, at least in part, in the second portion of the central bore of the collar member.