diff --git a/app/src/pages/PiperackModule.tsx b/app/src/pages/PiperackModule.tsx
index e2471fc..bfc1fd3 100644
--- a/app/src/pages/PiperackModule.tsx
+++ b/app/src/pages/PiperackModule.tsx
@@ -9,7 +9,8 @@ import { Piperack3D } from '@/components/three/Piperack3D';
 import SceneCapturePanel from '../components/SceneCapturePanel';
 import ExportMenu from '../components/ExportMenu';
 import { exportGenericToPDF, type GenericPDFSection } from '../lib/export-generic-pdf';
-import { Plus, Trash2, Layers } from 'lucide-react';
+import { Plus, Trash2, Layers, Info } from 'lucide-react';
+import { Tooltip, TooltipContent, TooltipTrigger, TooltipProvider } from '@/components/ui/tooltip';
 import { Input } from '@/components/ui/input';
 
 const PiperackModule: React.FC = () => {
@@ -192,8 +193,20 @@ const PiperackModule: React.FC = () => {
                     <Slider value={[numFrames]} min={1} max={5} step={1} onValueChange={v => setNumFrames(v[0])} />
                   </div>
                   <div className="space-y-2">
-                    <div className="flex justify-between">
-                      <span className="text-sm font-medium">Índice de Solidez (φ str)</span>
+                    <div className="flex justify-between items-center">
+                      <div className="flex items-center gap-2">
+                        <span className="text-sm font-medium">Índice de Solidez (φ str)</span>
+                        <TooltipProvider>
+                          <Tooltip>
+                            <TooltipTrigger asChild>
+                              <Info className="w-4 h-4 text-muted-foreground cursor-help" />
+                            </TooltipTrigger>
+                            <TooltipContent side="top" className="max-w-xs">
+                              <p>O índice de solidez (φ) representa a relação entre a área efetivamente bloqueada pelos perfis do reticulado e a área total contornada pelo pórtico. Quanto mais "fechado" for o pórtico estrutural, maior o arrasto aerodinâmico (ref. Tabela 28 da NBR 6123).</p>
+                            </TooltipContent>
+                          </Tooltip>
+                        </TooltipProvider>
+                      </div>
                       <span className="text-sm text-muted-foreground">{phiStruct.toFixed(2)}</span>
                     </div>
                     <Slider value={[phiStruct]} min={0.1} max={0.6} step={0.05} onValueChange={v => setPhiStruct(v[0])} />