Method of manufacturing post tensioning prefabricated building

Abstract

An improved post tensioning system for prefabricated building panels in which a concentric uniform radial compression is maintained in the slab. A post tensioning cable is placed in the concrete slab to form a perimeter loop starting from one corner of the slab to a point where the cable entered the slab and at a point turning 90.degree. to follow that portion of the cable in the periphery to a point midway up the Y axis and then turning 90.degree. across the X axis to bisect the slab and cross the opposite parallel portion of the cable to exit out the adjacent side of the slab. This creates a cable pattern with no less than 2.5 parallel cables in any direction.

Description

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention generally relates to prefabricated concrete building panels and, more particularly, to improvements in post tensioned concrete slabs in which there is a better distribution and an increase in compression forces in small slabs.

2. Background Description

In U.S. Pat. No. 4,432,175 issued to Rodney I. Smith discloses a post tensioned concrete slab in which one or more continuous reinforcement cables are positioned in a mold, around and near its outer periphery. These cables are lubricated and sheathed to prevent adherence to the concrete. The concrete is poured and cured, and each cable is post tensioned and anchored. The tensile force of each cable is therefore exerted toward the center of the slab as well as from side to opposite side. This results in a slab that can be relatively small and lightweight but has high strength, resistance to cracking and deterioration, and is relatively impermeable to liquids and gases.

While the prior design was, and continues to be, an excellent building product, the distribution of compressive forces tends to be strongly biased along one of the major axes of the panel. This is due to the rigid mold and straight line cable requirement of pretensioning and the single post tensioned perimeter loop design which exits strands at a single corner which attempts to provide uniform compression force in both principle axes of a small rectangular slab. This, in turn, meant that the product just met the criteria for post tensioning under the American Concrete Institute (ACI) guidelines. As a result, an improved design for the post tensioned building panel is highly desirable.

SUMMARY OF THE INVENTION

It is therefore an object of the invention to provide an improved post tensioning system for prefabricated concrete building panels of relatively small size where linear post tensioning would not work due to short cable lengths.

It is another object of the invention to provide a prefabricated concrete building panel in which the variation in compressive forces is reduced while the average compressive force is increased.

According to the invention, there is provided a prefabricated concrete construction panel which overcomes the limits of post tensioning as disclosed in U.S. Pat. No. 4,432,175. Specifically, by maintaining a concentric uniform radial compression in the slab, the benefits of limited crack size and amalgamated healing of the limited crack are realized due to the tendency of the concrete to reunite and form a new crystalline seal from the radial compression forces and continued presence of sufficient humidity in the concrete. In the practice of the invention, a post tensioning cable is placed in the concrete slab to form a perimeter loop starting from one corner of the slab to a point where the cable entered the slab and at a point turning 90.degree. to follow that portion of the cable in the periphery to a point midway up the Y axis and then turning 90.degree. across the X axis to bisect the slab and cross the opposite parallel portion of the cable to exit out the adjacent side of the slab. This creates a cable pattern with no less than 2.5 parallel cables in any direction and reduces concentrated forces in one corner of the slab.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing and other objects, aspects and advantages will be better understood from the following detailed description of a preferred embodiment of the invention with reference to the drawings, in which:

FIG. 1 is a plan view of a concrete building panel according to the invention;

FIGS. 2 and 3 are enlarged views of portions of FIG. 1 showing the tensioning of the cable;

FIG. 4 is a model of a 12'.times.10'.times.4" panel composed of 480 six inch squares using the new loop configuration according to the invention;

FIG. 5 is a stress contour map of a building panel made in accordance with the invention showing compression in the Y axis;

FIG. 6 is a stress contour map of the same building panel as in FIG. 4 showing compression in the X axis;

FIG. 7 is a model of a 12'.times.10'.times.4" panel composed of 480 six inch squares using the old loop configuration;

FIG. 8 is a stress contour map of a building panel modeled in FIG. 7 showing compression in the Y axis; and

FIG. 9 is a stress contour map of the same building panel as in FIG. 7 showing compression in the X axis.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT OF THE INVENTION

Referring now to the drawings, and more particularly to FIG. 1, there is shown a post tensioned concrete building panel indicated generally at 1 provided with a post tensioned cable 3 toward its outer periphery. The opposite ends of the cable 3 are secured by wedges 5 and 7.

The cable 3 forms a perimeter loop starting from one corner of the slab to a point where the cable entered the slab and at a point turning 90.degree. to follow the existing cable to a point midway up the Y axis and then turning 90.degree. across the X axis to bisect the slab and cross the opposite parallel cable to exit out the adjacent side of the slab. This creates a cable pattern with no less than 2.5 parallel cables in any direction. The cable 3 is preferably a hard drawn steel cable, but any flexible high-tensile strength material can be similarly employed.

The cable 3 is within a plastic sheath 15 which forms a channel extending around the periphery of the slab 1 and across the central portion of the slab 1. Cable 3 will be lubricated to facilitate its movement within sheath 15.

The post tensioning process is illustrated in FIGS. 2 and 3. When the concrete, which forms building panel 1 is poured, the sheath 15 and cable 3 are positioned so that the opposite ends of cable 3 extend outwardly from one corner (FIG. 2) and a side opposite that corner (FIG. 3). The one corner is provided with an anchor 17, such as the anchor component of the VSL S5N anchorage system. The anchor 17 has an aperture 19 in registry with a pocket 16 formed in the edge of the slab for access to the end of cable 3 and anchorage system 17 and 5. Likewise, as shown in FIG. 3, a second anchor 21 having an aperture 23 in registry with a pocket 22 formed in the edge of the slab for access to the opposite end of cable 3 and anchorage system 21 and 7 is provided in the side of the panel.

After the concrete has become relatively hardened (approximately twenty-four hours after it has been poured), there is an initial tensioning of the cable 3. This initial tensioning adds stripping strength to the slab that allows the mold to be removed more easily and with minimal surface deterioration. To accomplish this initial tensioning, the mold is removed and wedges 5 (FIG. 2) are applied to one end of the cable 3. The wedges are composed of two frustro-conically shaped halves which are partially inserted into an aperture and frictionally clamp the cable by means of teeth formed in the interior surfaces of the wedges.

With the wedges 5 gripping the one end of the cable 3, the other end of the cable is connected to a tensioning device 25, such as a hydraulic jack or similar device, for pulling the cable 3 in the direction indicated by the arrow in FIG. 3. A tensioning force is exerted on the cable 3 until an optimum stress in the cable is approximately equal to 0.7 F.sub.u (F.sub.u =270 kips per square inch (ksi)) is attained. This tensioning of the cable draws the wedges 5 into the aperture 19, thereby anchoring that end of the cable 3. While the cable is tensioned, the wedges 7 (FIG. 3) are applied to the end of the cable which extends beyond aperture 23. Tensioning device 25 is then released, and the tensile force of the cable 3 draws the wedges 7 into aperture 23, resulting in a final stress on the cable of 0.7 F.sub.u. The cable is trimmed and the pockets 16 and 22 are filled.

The tensioning process results in a post tensioned building panel which, due to the improved configuration of the cable 3, results in a better distribution of compression forces in small slabs less than twenty feet across. For such slabs, a finite analysis demonstrates the improved results of the present invention. The analysis of the new building panel configuration of the post-tensioned cable was performed on a finite-analysis program developed by DAST Consulting. The program input utilized the known stress/strain relationship and thermal coefficient of expansion and contraction of steel and a temperature delta to induce a given stress in the linear beam element presenting the post-tension cable. The concrete slab was modeled as a 12'.times.10'.times.4" thick plate composed of 480 six inch squares, as generally shown in FIG. 4. The model parameters were consistent with the limitations and requirements of ACI (American Concrete Institute) Standard 319-95, Chapter 18, "Prestress Concrete". Stresses were applied to both ends of the cable and friction loss due to bending of the post-tensioned cable was configured according to ACI guidelines. The computer generated stress contour maps for the building panel modeled as shown in FIG. 4 showing compression in the Y and X axes are shown in FIGS. 5 and 6 respectively, and the tabularized stress as shown in Table 1. The concrete slab of the cable configuration of U.S. Pat. No. 4,432,175 was also modeled as a 12'.times.10'.times.4" thick plate composed of 480 six inch squares, as generally shown in FIG. 7. The computer generated stress contour maps for the building panel modeled as shown in FIG. 7 showing compression in the Y and X axes are shown in FIGS. 8 and 9 respectively, and the tabularized stress as shown in Table 2.

TABLE 1__________________________________________________________________________STRESS VALUES (BY ELEMENT) - NEW LOOP CONFIGURATIONSx-x Sy-y Sx-x Sy-y Sx-x Sy-y Sx-x Sy-y Sx-x Sy-y__________________________________________________________________________1 -106 -47 51 -374 -155 101 24 -1312 151 -615 -483 201 19 -10182 -670 -2218 52 -388 -162 102 108 -1179 152 -593 -456 202 89 -9733 -671 -2203 53 -437 -482 103 292 -913 153 -561 -451 203 260 -8034 -86 -67 54 -356 -482 104 -655 -1032 154 -519 -462 204 -718 -10035 -77 -5 55 -398 -190 105 -517 -1014 155 -469 -478 205 -570 -10346 -116 -23 56 -468 -153 106 -581 -901 156 -420 -487 206 -632 -9867 112 -13 57 -44 -290 107 -596 -727 157 -370 -522 207 -652 -8568 14 21 58 -53 -74 108 -613 -597 158 -189 -474 208 -679 -7539 -2 27 59 15 -92 109 -605 -498 159 -131 -327 209 -675 -68110 -70 -13 60 4 -132 110 -598 -431 160 -16 -156 210 -623 -60811 -68 -39 61 -39 -1225 111 -588 -390 161 -15 -1075 211 -639 -54212 -7 -13 62 105 -1167 112 -572 -376 162 -73 -1014 212 -603 -49613 -148 -27 63 151 -1101 113 -556 -380 163 -220 -1050 213 -608 -48414 -203 24 64 231 -725 114 -547 -402 164 -283 -1114 214 -567 -47515 -159 -9 65 -326 -921 115 -526 -433 165 -472 -1088 215 -509 -48516 -185 -6 66 -794 -930 116 -523 -487 166 -545 -955 216 -432 -49817 -196 21 67 -635 -450 117 -489 -465 167 -584 -841 217 -330 -50918 -143 11 68 -503 -475 118 -658 -320 168 -673 -737 218 -192 -47819 -59 -9 69 -461 -437 119 234 -106 169 -628 -642 219 -72 -33120 -13 -14 70 -508 -312 120 45 -377 170 -632 -567 220 -18 -2921 -50 -723 71 -503 -131 121 8 -1240 171 -621 -513 221 9 -91522 240 -1556 72 -500 -287 122 55 -1153 172 -600 -483 222 22 -82323 185 -1497 73 -436 -376 123 206 -1110 173 -563 -475 223 -84 -81324 -206 -674 74 -462 -368 124 -716 -1208 174 -513 -482 224 -47 -103425 -246 -56 75 -569 -277 125 -559 -981 175 -451 -499 225 -718 -123726 -170 -35 76 -721 -626 126 -546 -903 176 -569 -522 226 -648 -97127 -123 -145 77 -310 -421 127 -584 -782 177 -252 -519 227 -745 -85028 -88 122 78 -141 -1 128 -606 -657 178 -152 -451 228 -715 -72729 -134 -143 79 6 -194 129 -618 -558 179 -80 -296 229 -708 -65430 -159 -118 80 -14 -195 130 -616 -486 180 -28 -57 230 -743 -66031 -181 -100 81 -23 -1307 131 -605 -440 181 7 -1061 231 -395 -55132 -207 -100 82 -78 -1112 132 -587 -419 182 53 -1031 232 -700 -50533 -232 143 83 -2 -1008 133 -563 -418 183 204 -1110 233 -663 -43934 -152 137 84 -31 -1112 134 -532 -433 184 -747 -1156 234 -626 -44735 -204 -113 85 -636 -1196 135 -501 -458 185 -587 -993 215 -586 -44936 -227 27 86 -572 -844 136 -473 -464 186 -573 -953 236 -543 -45337 -214 95 87 -651 -663 137 -503 -422 187 -612 -859 237 -486 -46338 -67 31 88 -594 -515 138 -678 -562 188 -635 -755 238 -381 -50139 -37 -53 89 -559 -446 139 196 -369 189 -639 -666 239 -150 -44340 -6 -59 90 -559 -373 140 37 -321 190 -639 -590 240 -15 -10541 93 -1057 91 -564 -327 141 -15 -1134 191 -630 -531 241 -3 -78342 234 -1278 92 -538 -332 142 -75 -1058 192 -609 -497 242 -22 -77343 231 -1184 93 -517 -356 143 -214 -1081 193 -572 -485 243 -5 -78644 10 -829 94 -535 -361 144 -275 -1130 194 -528 -489 244 110 -57545 -10 -86 95 -582 -418 145 -465 -1086 195 -461 -504 245 -414 -97646 -523 -11 96 -517 -472 146 -537 -939 196 -368 -521 246 -899 -113047 427 -282 97 -617 -655 147 -576 -815 197 -257 -516 247 -780 -70048 381 -549 98 -33 -404 148 -605 -704 198 -147 -452 248 -700 -74149 400 -519 99 -98 -181 149 -622 -607 199 -56 -292 249 -705 -70250 370 -179 100 1 -253 150 -624 -532 200 7 -19 250 -829 -443 -166251 0 0 301 -320 -505 351 -677 -298 401 -20 -256 451 -432 -32252 -792 -330 302 -93 -582 352 -678 -328 402 -16 -272 452 -443 -66253 -718 -424 303 -165 -588 353 -679 -368 403 98 -63 453 -465 -125254 -682 -414 304 -284 -537 354 -677 -412 404 -421 -388 454 -485255 -666 -411 305 -408 -476 355 -677 -462 405 -761 -658 455 -189 140256 -667 -400 306 -461 -449 456 -670 -501 406 -587 -483 456 -189 -241 -110257 -689 -383 307 -490 -392 357 -691 -517 407 -554 -469 457 -227 -16258 -723 -395 308 -602 -304 358 -807 -701 408 -657 -306 458 -99 -13259 -686 -579 309 -641 -283 359 162 -516 409 -653 -161 459 -51 -54260 -73 -369 310 -626 -346 360 26 414 410 -647 -130 460 -9 -42261 -5 -671 311 -651 -392 361 44 -571 411 -647 -133 461 -11 -11262 -14 -701 312 -671 -394 362 23 -281 412 -654 -171 462 -57 -12263 -24 -665 313 -687 -399 -63 -733 -455 413 -657 -323 463 -150 -2 - 264 -131 -630 314 -711 -404 364 -563 -525 41 4 -548 -485 464 -252 - 18265 -73 -207 315 -733 -409 165 -596 -521 415 -575 -500 465 -362 0266 -673 -297 316 -757 -429 366 -589 -447 416 -732 -669 466 -536 49267 -653 -602 317 -765 -447 367 -613 -386 417 -397 -401 467 -519 43268 -660 -865 318 -787 -483 368 -636 -319 418 -107 -67 468 -370 14269 -773 -822 319 -739 -682 369 -663 -267 419 -8 -237 469 -382 -26270 -751 -519 320 -97 -476 370 -682 -242 420 -17 -187 470 -244 -6271 -401 -476 321 -21 -507 371 -687 -251 421 -315 -151 471 -235 -6272 -758 -491 322 -158 -554 372 -679 -291 422 -16 -127 472 -255 -25273 -725 -398 323 -232 -593 373 -667 -350 423 -127 -119 473 -352 -15274 -716 -400 324 -424 -565 374 -659 -418 424 -77 118 474 -454 39275 -723 -389 325 -460 -480 375 -646 -478 425 -517 -29 475 -466 46276 -759 -367 326 -504 -436 376 -650 -554 426 -468 -683 476 -295 -1277 -846 -329 327 -556 -380 377 -598 -560 427 -677 -683 477 -199 -2278 -1027 -269 328 -608 -326 378 -734 -467 428 -604 -160 478 -116 -2279 -1393 -253 329 -643 -303 379 -221 -237 429 -582 -106 479 -42 -10280 -2176 -1069 330 -655 -315 380 -46 -423 430 -570 -78 480 -8 -8281 -7 -572 331 -659 -341 381 -3 -376 431 -568 -79282 -38 -627 332 -675 -363 382 -714 -305 432 -578 -110 AVERAGE -397.925 -452.246283 -107 -624 333 -685 -383 383 -62 -502 433 -600 -166 AVEDEV 271.1039 256.7913284 -180 -511 334 -695 -408 384 -715 -714 434 -679 -684285 -386 -402 335 -705 -435 385 -597 -516 435 -411 -680 COMBIN.286 -459 -421 336 -716 -465 386 -625 -485 436 -470 -51 AVERAGE: -425287 -500 -510 337 -705 -556 387 -607 -398 437 -49 99288 -511 -199 338 -498 -640 388 -634 -314 438 -104 -117289 -641 -182 339 -261 -600 389 -671 -230 439 -6 -105290 -623 -448 340 -27 326 390 -680 -187 440 0 -113291 -660 -433 341 36 -595 391 -682 -193 441 -12 -57292 -650 -422 342 196 -530 392 -678 -247 442 -65 -65293 -706 -419 343 -745 -656 393 -645 -338 443 -127 -13294 -722 -397 344 -568 -479 394 -622 -425 444 -271 -8295 -743 -391 345 -534 -479 395 -639 -512 445 -297 -100296 -783 -379 346 -557 -439 396 -604 -544 446 -257 -254297 -869 -351 347 -588 -380 397 -705 -729 447 -496 -224298 -1049 -299 348 -625 -327 398 -60 -499 448 -481 -126299 -1404 -289 349 -654 -292 399 -106 -261 449 -456 -67300 -2179 -1101 350 -671 -283 400 1 -270 450 -437 -32__________________________________________________________________________ TABLE 2__________________________________________________________________________STRESS VALUES (BY ELEMENT) - ORIGINAL LOOP CONFIGURATIONSx-x Sy-y Sx-x Sy-y Sx-x Sy-y Sx-x Sy-y Sx-x Sy-y__________________________________________________________________________1 -138 -138 51 -496 -83 101 -11 -520 151 -355 -391 201 -1 -2812 -1307 -2253 52 -511 -120 102 -42 -667 152 -349 -413 202 -9 -3673 -1506 -2104 53 -538 -176 103 -133 -690 153 -339 -440 203 -26 -434 -895 -36 54 -616 -696 104 -247 -613 154 -327 -470 204 -53 -4765 -632 -2 55 -423 -693 105 -333 -503 155 -314 -495 205 -88 -4966 -513 -11 56 -482 -31 106 -392 -404 156 -310 -509 206 -127 -5007 -431 -1 57 -53 -121 107 -430 -328 157 -305 -555 207 -166 -4928 -371 -3 58 -113 -113 108 -451 -279 158 -160 -532 208 -201 -4779 -327 -3 59 -11 -123 109 -461 -255 159 -128 -445 209 -231 -47710 -299 -4 60 -2 -155 110 -466 -254 160 -14 -373 210 -229 -49811 -289 -7 61 -36 -898 111 -467 -275 161 -2 -339 211 -228 -52012 -390 -28 62 -580 -1064 112 -459 -318 162 -13 -427 212 -220 -51513 -383 -15 63 -597 -791 113 -449 -375 163 -39 -485 213 -216 -50614 -526 -41 64 -599 -597 114 -448 -436 164 -80 -509 214 -180 -51215 -539 -48 65 -620 -402 115 -451 -482 165 -130 -505 215 -141 -52616 -366 0 66 -617 -250 116 -488 -535 166 -182 -485 216 -101 -52417 -257 -18 67 -584 -165 117 -485 -516 167 -229 -459 217 -63 -49818 -155 -1 68 -551 -127 118 -685 -420 168 -265 -438 218 -32 -44219 -60 -12 69 -530 -113 119 -253 -234 169 -289 -428 219 -11 -35320 -12 -12 70 -521 -117 120 -49 -539 170 -300 -429 220 -1 -23321 -2251 -1307 71 -523 -139 121 -1 -440 171 -302 -439 221 -1 -26322 -1227 -1229 72 -536 -183 122 -26 -555 172 -296 -453 222 -8 -35423 -888 -1201 73 -550 -332 123 -79 -599 173 -284 -471 223 -24 -42524 -1064 -579 74 -461 -492 124 -156 -577 174 -265 -491 224 -50 -47225 -846 -97 75 -510 -499 125 -236 -516 175 -241 -511 225 -83 -49726 -667 -42 76 -702 -665 126 -301 -446 17 -209 -533 226 -120 -50427 -557 -27 77 -380 -383 127 -350 -387 177 -147 -535 227 -55 -50128 -485 -20 78 -122 -53 128 -382 -345 178 -100 -494 228 -185 -18929 -441 -19 79 -6 -261 129 -402 -323 179 -66 -410 229 -209 -46030 -420 -23 80 -18 -258 130 -411 -321 180 -26 -287 230 -247 -51631 -420 -34 81 -2 -637 131 -412 -336 181 -2 -306 231 -194 -57932 -434 -74 82 -98 -846 132 -406 -367 182 -11 -391 232 -240 -53233 -456 -134 83 -300 -789 133 -597 -407 183 -31 -453 231 -190 -48334 -469 -219 84 -403 -617 134 -389 -448 184 -63 -488 234 -158 -51835 -240 -250 85 -465 -465 135 -391 -487 185 -104 -499 235 -121 -52836 -283 -100 86 -502 -340 136 -401 -499 186 -148 -493 236 -84 -52037 -262 -6 87 -515 -253 137 -472 -468 187 -191 -478 237 -49 -48938 -123 -10 88 -513 -204 138 -686 -617 188 -227 -465 238 -22 -40339 -64 -64 89 -509 -182 139 223 -467 189 -250 -461 239 -6 -34140 -12 -60 90 -507 -183 140 42 -523 190 -259 -469 240 -1 -22741 -2101 -1507 91 -509 -205 141 -3 -383 191 -256 -480 241 -1 -25242 -1200 -888 92 -510 -264 142 -17 -479 192 -252 -488 242 -9 -35143 -849 -848 93 -486 -353 143 -54 -532 193 -240 -495 243 -27 -42744 -793 -596 94 -479 -433 144 -108 -53 194 -16 -507 244 -55 -47645 -792 -299 95 -518 -509 145 -171 -513 195 -181 -522 245 -89 -50146 -695 -134 96 -513 -526 146 -232 -471 196 -137 -529 246 -126 -50947 -607 -83 97 -656 -707 147 -282 -430 197 -95 -513 247 -161 -50348 -547 -62 98 -28 -481 148 -318 -398 198 -58 -464 248 -189 -49349 -510 -56 99 -99 -281 149 -342 -381 199 -24 -378 249 -209 -47750 -494 -60 100 -1 -367 150 -353 -380 200 -5 -249 250 -220 -263251 0 0 301 -27 -288 351 -132 -349 401 -18 -254 451 -370 -38252 -208 -271 302 -68 -408 352 -424 -369 402 -6 -258 452 -387 -71253 -186 -499 303 -105 -488 353 -412 -402 403 -120 249 453 -413 -110254 -156 -519 304 -155 -525 354 -401 -439 404 -384 -378 454 -431 -210255 -122 -526 305 -219 -520 355 -400 -477 405 -707 -660 455 -207 -246256 -84 -519 306 -254 -495 356 -406 -491 406 -508 -492 456 -264 -90257 -49 -189 307 -283 -473 357 -473 -462 407 -459 -483 457 -249 0258 -22 -429 308 -307 -453 358 -686 -613 408 -542 -324 458 -118 -9259 -6 --340 309 -321 -443 359 223 -461 409 -531 -183 459 -62 -61260 -1 -226 310 -324 -445 360 42 -515 410 -521 -150 460 -12 -57261 -2 -248 311 -318 451 361 48 -533 411 -521 -150 461 -12 -12262 -14 -359 312 -313 -457 362 252 -232 412 -529 -183 462 -59 -12263 -37 -438 313 -301 -466 363 -689 -417 413 -539 -324 463 -152 -1264 -71 -486 314 -280 -482 364 -490 -509 414 -447 -479 464 -250 -16265 -109 -509 315 -250 -502 365 -495 -526 415 -489 -487 465 -351 0266 -149 -510 316 -214 -526 366 -462 -470 416 -668 -665 466 -510 -48267 -185 -501 317 -150 -529 367 -462 -424 417 -400 -394 467 -487 -42268 -214 -485 318 -101 -489 368 -465 -366 418 -114 -46 468 -325 -14269 -237 -452 319 -66 -405 369 -477 -317 419 -9 -254 469 -235 -29270 -276 -510 320 -26 -281 370 -486 -288 420 -18 -249 470 -201 -8271 -211 -568 321 -15 -370 371 -484 -289 421 -1 -153 471 -200 -7272 -263 -520 322 -130 -440 372 -473 -320 422 -11 -120 472 -233 -27273 -213 -472 323 -165 -524 373 -459 -369 423 -113 -109 473 -319 -15274 -180 -510 324 -312 -545 374 -456 -425 424 -55 -127 474 -472 -40275 -143 -524 325 -320 -497 375 -456 -471 425 -488 -23 475 -500 -48276 -103 -521 326 -329 -480 376 -489 -528 426 -439 -691 476 -344 -2277 -65 -496 327 -346 -455 377 -484 -513 427 -576 -688 477 -245 -16278 -32 -440 328 -361 -427 378 -684 -417 428 -508 -174 478 -148 -1279 -12 -350 329 -373 -408 379 253 -229 429 -486 -120 479 -57 -12280 -2 -230 330 -377 -400 380 48 -530 430 -475 -90 480 -11 -11281 -6 -256 331 -375 -403 381 0 -362 431 -475 -90282 -27 -379 332 -368 -415 382 -100 -277 432 -487 -118 AVERAGE: -293 -375283 -64 -460 333 -356 -416 383 -30 -477 433 -512 -171 AVEDEV: 194 176284 -103 -503 334 -341 -462 384 -660 -702 434 -587 -678285 -147 -516 335 -324 -485 385 -517 -519 435 -389 -676 COMBIN.286 -192 -507 336 -316 -501 386 -523 -500 436 -438 -10 AVERAGE: -334287 -227 -490 337 -307 -549 387 -486 -423 437 -66 -134288 -256 -469 338 -161 -526 388 -495 -344 438 -117 -107289 -283 -465 339 -128 -439 389 -520 -263 439 -12 -117290 -275 -482 340 -14 -366 390 -521 -218 440 -2 -149291 -273 -500 341 -42 -518 391 -520 -219 441 -12 -59292 -263 -493 342 -221 -459 392 -516 -264 442 -63 -62293 -260 -486 343 -689 -608 393 -489 -345 443 -121 -8294 -224 -495 344 -478 -459 394 -477 -421 444 -260 -2295 -186 -517 345 -411 -488 395 -513 -498 445 -283 -94296 -141 -525 346 -405 -474 396 -509 -521 446 -246 -250297 -97 -509 347 -407 -435 397 -651 -708 447 -415 -224298 -60 -460 348 -418 -397 398 -31 -481 448 -408 -135299 -25 -374 349 -428 -365 399 -101 -274 449 -386 -75300 -5 -245 350 -434 -348 400 0 -357 450 -370 -38__________________________________________________________________________

As can be seen from Tables 1 and 2, a considerable improvement has been achieved with the new concrete building panel configuration. First, there has been a reduction in variation in compressive stress values between the Y and X axes from 28% to 14%. At the same time the increase in the average pre-compressive force with the new cable configuration is a 27% increase (from 334 psi to 425 psi) over the pattern achieved in the concrete building panel of U.S. Pat. No. 4,432,175. The increased pre-compression force further enhances the concrete building panel in the following areas:

1. Allowable load capacity in flexure--ACI 18.7.1 2. Resist punching shear--ACI 11.12.2.2 3. Reduced deflection--ACI 9.5.4.1 4. Enhanced Autogenous Healing (Neville'publication Properties of Concrete, Fourth Edition)

While the invention has been described in terms of a single preferred embodiment, those skilled in the art will recognize that the invention can be practiced with modification within the spirit and scope of the appended claims.

Claims

1. A method of manufacturing a post tensioned prefabricated concrete building panel comprising the steps of:

positioning a cable member around a perimeter and through a central portion of a mold such that the cable member has no less than 2.5 parallel portions of the cable member in any direction;

pouring concrete into the mold to form the concrete building panel;

removing the mold from the concrete building panel;

exerting a predetermined tensioning force on the cable member after the removing step; and

securing a first end of the cable member at a corner of the concrete building panel and a second end of the cable member at a side of the concrete building panel which opposes the corner after exerting the predetermined tensioning force.

2. The method of manufacturing a post tensioned prefabricated concrete building panel recited in claim 1 further comprising the step of initially tensioning the cable member after the concrete has become relatively hardened and prior to removing the mold.

3. The method of manufacturing a post tensioned prefabricated concrete building panel recited in claim 1 wherein the predetermined tensioning force puts a stress in the cable member of approximately 0.7 F.sub.u or 270 kips per square inch (ksi).

4. The method of manufacturing a post tensioned prefabricated concrete building panel recited in claim 1 wherein the step of positioning the cable member results in a pattern in which the cable member starts from one corner of the concrete building panel to a point where the cable member entered the concrete building panel and at a point turning 90.degree. to follow the cable member to a point midway up a Y axis of the concrete building panel and then turning 90.degree. across a X axis of the concrete building panel to bisect the concrete building panel and cross an opposite parallel portion of the cable member to exit out an adjacent side of the concrete building panel.

5. The method of manufacturing a post tensioned prefabricated concrete building panel recited in claim 1 wherein the step of positioning the cable member includes positioning a portion of the cable member between opposing sides of the cable member within the mold.

6. The method of manufacturing a post tensioned prefabricated concrete building panel recited in claim 1 wherein the step of positioning the cable member includes positioning the cable member parallel to at least one side of the mold in any direction.

7. The method of manufacturing a post tensioned prefabricated concrete building panel recited in claim 1 wherein the step of positioning the cable member includes positioning the cable member such that the cable member has 2.5 parallel portions of the cable member in a first direction and 3 parallel portions of the cable member in a second direction perpendicular to the first direction.