Bélidor, Bernard Forest de, La science des ingenieurs dans la conduite des travaux de fortification et d' architecture civile

Table of Notes

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              <s xml:id="echoid-s2168" xml:space="preserve">
                <pb o="11" file="0119" n="122" rhead="LIVRE II. DE LA MECANIQUE DES VOUTES."/>
              & </s>
              <s xml:id="echoid-s2169" xml:space="preserve">la clef; </s>
              <s xml:id="echoid-s2170" xml:space="preserve">ainſi ayant une Voûte en plain ceintre BDI, dont cha-
                <lb/>
              que quart de cercle BD & </s>
              <s xml:id="echoid-s2171" xml:space="preserve">DI, ſoit diviſé en deux également au point
                <lb/>
                <note position="right" xlink:label="note-0119-01" xlink:href="note-0119-01a" xml:space="preserve">
                  <emph style="sc">Fig</emph>
                . 7.</note>
              C & </s>
              <s xml:id="echoid-s2172" xml:space="preserve">H, l’experience montre que c’eſt toûjours aux endroits FC & </s>
              <s xml:id="echoid-s2173" xml:space="preserve">
                <lb/>
              H &</s>
              <s xml:id="echoid-s2174" xml:space="preserve">c. </s>
              <s xml:id="echoid-s2175" xml:space="preserve">que la Voûte ſe deſunit quand ſa pouſſée eſt au-deſſus de la
                <lb/>
              réſiſtance des piés-droits. </s>
              <s xml:id="echoid-s2176" xml:space="preserve">Or, puiſque le plus foible d’une Voûte eſt
                <lb/>
              vers le milieu des reins, il eſt donc naturel de ſupoſer que c’eſt-là
                <lb/>
              où ſe fait toute l’action de la pouſſée, & </s>
              <s xml:id="echoid-s2177" xml:space="preserve">de conſiderer les deux par-
                <lb/>
              ties de la Voûte CG & </s>
              <s xml:id="echoid-s2178" xml:space="preserve">CE, (que nous nommerons vouſſoirs) comme
                <lb/>
              ne compoſant qu’une ſeule pierre, chacune en particulier, dont l’une
                <lb/>
              CE eſt parfaitement liée avec ſon pié-droit BP, & </s>
              <s xml:id="echoid-s2179" xml:space="preserve">l’autre CG agit
                <lb/>
              comme un coin qui ſeroit introduit entre les deux plans FA & </s>
              <s xml:id="echoid-s2180" xml:space="preserve">GA
                <lb/>
              pour les ſéparer; </s>
              <s xml:id="echoid-s2181" xml:space="preserve">ou bien l’on pourra prendre toute la partie ſupe-
                <lb/>
              rieure CGH de la Voûte, qui tend à ſéparer comme un coin les deux
                <lb/>
              Plans AF & </s>
              <s xml:id="echoid-s2182" xml:space="preserve">A &</s>
              <s xml:id="echoid-s2183" xml:space="preserve">c. </s>
              <s xml:id="echoid-s2184" xml:space="preserve">& </s>
              <s xml:id="echoid-s2185" xml:space="preserve">dans ce ſens, ce ſera cette partie qui cauſera
                <lb/>
              toute la pouſſée; </s>
              <s xml:id="echoid-s2186" xml:space="preserve">la moitié CG agira pour écarter le corps P FCS,
                <lb/>
              (compoſé du pié-droit PB & </s>
              <s xml:id="echoid-s2187" xml:space="preserve">du vouſſoir EC, comme je l’ai inſi-
                <lb/>
              nué d’abord) & </s>
              <s xml:id="echoid-s2188" xml:space="preserve">alors il ſuffira pour calculer cette pouſſée de n’a-
                <lb/>
              voir égard qu’à la moitié de la Voûte depuis le point d’apui P, juſ-
                <lb/>
              qu’au ſommet DG, puiſque l’on concevra la même choſe pour l’au-
                <lb/>
              tre moitié.</s>
              <s xml:id="echoid-s2189" xml:space="preserve"/>
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            <p>
              <s xml:id="echoid-s2190" xml:space="preserve">Conſidérant le vouſſoir ſupérieur FD, comme n’ayant aucune
                <lb/>
              liaiſon avec le reſte de la maçonnerie, la pouſſée qui ſe fera à l’é-
                <lb/>
              gard du point d’apui P, ſera la plus grande qu’il eſt poſſible; </s>
              <s xml:id="echoid-s2191" xml:space="preserve">puiſ-
                <lb/>
              que dans une Voûte il n’arrive jamais que les vouſſoirs agiſſent
                <lb/>
              auſſi puiſſamment qu’ils feroient ſi leurs joints étoient extrêmement
                <lb/>
              polis, ſans trouver d’obſtacle de la part du mortier ni du frotement:
                <lb/>
              </s>
              <s xml:id="echoid-s2192" xml:space="preserve">par conſéquent ſi l’on cherche à proportionner la réſiſtance du pié-
                <lb/>
              droit P B à cette plus grande pouſſée, on donnera à la puiſſance
                <lb/>
              réſiſtante une force un peu au-deſſus de celle qu’il lui faudroit effec-
                <lb/>
              tivement pour ſoûtenir l’effort du vouſſoir FD, dans le cas où il
                <lb/>
              ſeroit lié avec le reſte de la Voûte; </s>
              <s xml:id="echoid-s2193" xml:space="preserve">ainſi cette ſupoſition ne pou-
                <lb/>
              vant que contribuer à la fermeté des piés-droits, il s’enſuit que
                <lb/>
              conſidérer ici les choſes dans la rigueur de la Théorie, c’eſt leur
                <lb/>
              donner tout l’avantage qu’on peut déſirer dans la pratique.</s>
              <s xml:id="echoid-s2194" xml:space="preserve"/>
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            <p>
              <s xml:id="echoid-s2195" xml:space="preserve">Cela poſé, ſi l’on éleve une perpendiculaire LO ſur le milieu du
                <lb/>
              joint FC, cette perpendiculaire exprimera la direction de la puiſ-
                <lb/>
              ſance qui ſoûtiendroit l’effort que fait le vouſſoir FD, ſur le plan
                <lb/>
              incliné F A ; </s>
              <s xml:id="echoid-s2196" xml:space="preserve">de même ſi ſur le milieu du joint GD on éleve une
                <note symbol="*" position="right" xlink:label="note-0119-02" xlink:href="note-0119-02a" xml:space="preserve">Art. 1.</note>
              autre perpendiculaire HW, elle exprimera auſſi la direction de la
                <lb/>
              puiſſance qui ſoûtiendroit l’effort que feroit le vouſſoir contre le
                <lb/>
              Plan vertical G A: </s>
              <s xml:id="echoid-s2197" xml:space="preserve">enfin ſi du point X, (que je ſupoſe le centre </s>
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